Whether double floats can silently have 80 bit accumulators is a controversial thing. Numerical analysis people like it. Computer science types seem not to because it's unpredictable. I lean towards, "we should have it, but it should be explicit", but this is not the most considered opinion. I think there's a legitimate reason why Intel included it in x87, and why DSPs include it.
During an internship in 1986 I wrote C code for a machine with 10-bit bytes, the BBN C/70. It was a horrible experience, and the existence of the machine in the first place was due to a cosmic accident of the negative kind.
I think the pdp-10 could have 9 bit bytes, depending on decisions you made in the compiler. I notice it's hard to Google information about this though. People say lots of confusing, conflicting things. When I google pdp-10 byte size it says a c++ compiler chose to represent char as 36 bits.
I like the Rust approach more: usize/isize are the native integer types, and with every other numeric type, you have to mention the size explicitly.
On the C++ side, I sometimes use an alias that contains the word "short" for 32-bit integers. When I use them, I'm explicitly assuming that the numbers are small enough to fit in a smaller than usual integer type, and that it's critical enough to performance that the assumption is worth making.
This doesn't feel like a serious question, but in case this is still a mystery to you… the name bit is a portmanteau of binary digit, and as indicated by the word "binary", there are only two possible digits that can be used as values for a bit: 0 and 1.
Me? I just dabble with documenting an unimplemented "50% more bits per byte than the competition!" 12-bit fantasy console of my own invention - replete with inventions such as "UTF-12" - for shits and giggles.
They can just target C++23 or earlier, right? I have a small collection of SHARCs but I am not going to go crying to the committee if they make C++30 (or whatever) not support CHAR_BIT=32
TI DSP Assembler is pretty high level, it's "almost C" already.
Writing geophysical | military signal and image processing applications on custom DSP clusters is suprisingly straightforward and doesn't need C++.
It's a RISC architecture optimised for DSP | FFT | Array processing with the basic simplification that char text is for hosts, integers and floats are at least 32 bit and 32 bits (or 64) is the smallest addressable unit.
Fantastic architecture to work with for numerics, deep computational pipelines, once "primed" you push in raw aquisition samples in chunks every clock cycle and extract processed moving window data chunks every clock cycle.
A single ASM instruction in a cycle can accumulate totals from vector multiplication and modulo update indexes on three vectors (two inputs and and out).
Don’t break perfection!! Just accumulate more perfection.
What we need is a new C++ symbol that reliably references eight bit bytes, without breaking compatibility, or wasting anny opportunity to expand the kitchen sink once again.
I propose “unsigned byte8” and (2’s complement) “signed byte8”. And “byte8” with undefined sign behavior because we can always use some more spice.
“unsigned decimal byte8” and “signed decimal byte8”, would limit legal values to 0 to 10 and -10 to +10.
“unsigned centimal byte8” and “signed centimal byte8”, would limit legal values to 0 to 100 and -100 to +100.
Signed integers did not have to be 2’s complement, there were 3 valid representations: signed mag, 1s and 2s complement. Modern C and C++ dropped this and mandate 2s complement (“as if” but that distinction is moot here, you can do the same for CHAR_BIT). So there is certainly precedence for this sort of thing.
Well then someone somewhere with some mainframe got so angry they decided to write a manifesto to condemn kids these days and announced a fork of Qt because Qt committed the cardinal sin of adopting C++20. So don’t say “a problem literally nobody has”, someone always has a use case; although at some point it’s okay to make a decision to ignore them.
> because Qt committed the carnal sin of adopting C++20
I do believe you meant to write "cardinal sin," good sir. Unless Qt has not only become sentient but also corporeal when I wasn't looking and gotten close and personal with the C++ standard...
I'm totally fine with enforcing that int8_t == char == 8-bits, however I'm not sure about spreading the misconception that a byte is 8-bits. A byte with 8-bits is called an octet.
At the same time, a `byte` is already an "alias" for `char` since C++17 anyway[1].
Possible, but likely slow. There's nothing in the "C abstract machine" that mandates specific hardware. But, the bitshift is only a fast operation when you have bits. Similarly with bitwise boolean operations.
So please do excuse my ignorance, but is there a "logic" related reason other than hardware cost limitations ala "8 was cheaper than 10 for the same number of memory addresses" that bytes are 8 bits instead of 10? Genuinely curious, as a high-level dev of twenty years, I don't know why 8 was selected.
To my naive eye, It seems like moving to 10 bits per byte would be both logical and make learning the trade just a little bit easier?
One example from the software side: A common thing to do in data processing is to obtain bit offsets (compression, video decoding etc.). If a byte would be 10 bits you would need mod%10 operations everywhere which is slow and/or complex. In contrast mod%(2^N) is one logic processor instruction.
I'm fairly sure it's because the English character set fits nicely into a byte. 7 bits would have have worked as well, but 7 is a very odd width for something in a binary computer.
One thought is that it's always a whole number of bits (3) to bit-address within a byte. It's 3.5 bits to bit address a 10 bit byte. Sorta just works out nicer in general to have powers of 2 when working on base 2.
Another part of it is the fact that it's a lot easier to represent stuff with hex if the bytes line up.
I can represent "255" with "0xFF" which fits nice and neat in 1 byte. However, now if a byte is 10bits that hex no longer really works. You have 1024 values to represent. The max value would be 0x3FF which just looks funky.
Coming up with an alphanumeric system to represent 2^10 cleanly just ends up weird and unintuitive.
Many circuits have ceil(log_2(N_bits)) scaling wrt to propagation delay/other dimensions so you’re just leaving efficiency on the table if you aren’t using a power of 2 for your bit size.
Because modern computing has settled on the Boolean (binary) logic (0/1 or true/false) in the chip design, which has given us 8 bit bytes (a power of two). It is the easiest and most reliable to design and implement in the hardware.
On the other hand, if computing settled on a three-valued logic (e.g. 0/1/«something» where «something» has been proposed as -1, «undefined»/«unknown»/«undecided» or a «shade of grey»), we would have had 9 bit bytes (a power of three).
10 was tried numerous times at the dawn of computing and… it was found too unwieldy in the circuit design.
> On the other hand, if computing settled on a three-valued logic (e.g. 0/1/«something» where «something» has been proposed as -1, «undefined»/«unknown/undecided» or a «shade of grey»), we would have had 9 bit bytes (a power of three).
Is this true? 4 ternary bits give you really convenient base 12 which has a lot of desirable properties for things like multiplication and fixed point. Though I have no idea what ternary building blocks would look like so it’s hard to visualize potential hardware.
It is hard to say whether it would have been 9 or 12, now that people have stopped experimenting with alternative hardware designs. 9-bit byte designs certainly did exist (and maybe even the 12-bit designs), too, although they were still based on the Boolean logic.
I have certainly heard an argument that ternary logic would have been a better choice, if it won over, but it is history now, and we are left with the vestiges of the ternary logic in SQL (NULL values which are semantically «no value» / «undefined» values).
If you're ignoring what's efficient to use then just use a decimal data type and let the hardware figure out how to calculate that for you best. If what's efficient matters then address management, hardware operation implementations, and data packing are all simplest when the group size is a power of the base.
likely mostly as a concession to ASCII in the end. you used a typewriter to write into and receive terminal output from machines back in the day. terminals would use ASCII. there were machines with all sorts of smallest-addressable-sizes, but eight bit bytes align nicely with ASCII. makes strings easier. making strings easier makes programming easier. easier programming makes a machine more popular. once machines started standardizing on eight bit bytes, others followed. when they went to add more data, they kept the byte since code was written for bytes, and made their new registeres two bytes. then two of those. then two of those. so we're sitting at 64 bit registers on the backs of all that that came before.
This would be a great setup for a time travelling science fiction where there is some legacy UNIVAC software that needs to be debugged, and John Titor, instead of looking for an IBM 5100, came back to the year 2024 to find a pre-P3477R0 compiler.
They still exist. You can still run OS 2200 on a Clearpath Dorado.[1] Although it's actually Intel Xeon processors doing an emulation.
Yes, indexing strings of 6-bit FIELDATA characters was a huge headache. UNIVAC had the unfortunate problem of having to settle on a character code in the early 1960s, before ASCII was standardized. At the time, a military 6-bit character set looked like the next big thing. It was better than IBM's code, which mapped to punch card holes and the letters weren't all in one block.
idk. by today most software already assumes 8 bit == byte in subtle ways all over the place to a point you kinda have to use a fully custom or at least fully self reviewed and patched stack of C libraries
so delegating such by now very very edge cases to non standard C seems fine, i.e. seems to IMHO not change much at all in practice
and C/C++ compilers are anyway full of non standard extensions and it's not that CHAR_BIT go away or you as a non-standard extension assume it might not be 8
> most software already assumes 8 bit == byte in subtle ways all over the place
Which is the real reason why 8-bits should be adopted as the standard byte size.
I didn't even realize that the byte was defined as anything other than 8-bits until recently. I have known, for decades, that there were non-8-bit character encodings (including ASCII) and word sizes were all over the map (including some where word size % 8 != 0). Enough thought about that last point should have helped me realize that there were machines where the byte was not 8-bits, yet the rarity of encountering such systems left me with the incorrect notion that a byte was defined as 8-bits.
Now if someone with enough background to figure it out doesn't figure it out, how can someone without that background figure it out? Someone who has only experienced systems with 8-bit bytes. Someone who has only read books that make the explicit assumption of 8-bit bytes (which virtually every book does). Anything they write has the potential of breaking on systems with a different byte size. The idea of writing portable code because the compiler itself is "standards compliant" breaks down. You probably should modify the standard to ensure the code remains portable by either forcing the compiler for non-8-bit systems to handle the exceptions, or simply admitting that compiler does not portable code for non-8-bit systems.
The UNIVAC 1108 (and descendants) mainframe architecture was not discontinued in 1986. The company that owned it (Sperry) merged with Burroughs in that year to form Unisys. The platform still exists, but now runs as a software emulator under x86-64. The OS is still maintained and had a new release just last year. Around the time of the merger the old school name “UNIVAC” was retired in a rebranding, but the platform survived.
Its OS, OS 2200, does have a C compiler. Not sure if there ever was a C++ compiler, if there once was it is no longer around. But that C compiler is not being kept up to date with the latest standards, it only officially supports C89/C90 - this is a deeply legacy system, most application software is written in COBOL and the OS itself itself is mainly written in assembler and a proprietary Pascal-like language called “PLUS”. They might add some features from newer standards if particularly valuable, but formal compliance with C99/C11/C17/C23/etc is not a goal.
The OS does contain components written in C++, most notably the HotSpot JVM. However, from what I understand, the JVM actually runs in x86-64 Linux processes on the host system, outside of the emulated mainframe environment, but the mainframe emulator is integrated with those Linux processes so they can access mainframe files/data/apps.
On RISC machines, it can be very useful to have the concept of "words," because that indicates things about how the computer loads and stores data, as well as the native instruction size. In DSPs and custom hardware, it can indicate the only available datatype.
The land of x86 goes to great pains to eliminate the concept of a word at a silicon cost.
I'm saying the term "Word" abstracting the number of bytes a CPU can process in a single operation is an outdated concept. We don't really talk about word-sized values anymore. Instead we mostly explicit on the size of value in bits. Even the idea of a CPU having just one relevant word size is a bit outdated.
There were/are C++ compilers for PDP-10 (9 bit byte). Those haven't been maintained AFAICT, but there are C++ compilers for various DSP's where the smallest unit of access is 16 or 32 bits that are still being sold.
Why? Pls no. We've been told (in school!) that byte is byte. Its only sometimes 8bits long (ok, most of the time these days). Do not destroy the last bits of fun.
Is network order little endian too?
Why can’t it be 8?, the fact that it’s a trit doesn’t put any constraint on the byte (tryte ? size). You could actually make it 5 or 6 trits (~9.5 bits) for similar information density. The Setun used 6 trit addressable units.
Here's a bit of 40 year old code I wrote which originally ran on 36-bit PDP-10 machines, but will work on non-36 bit machines.[1] It's a self-contained piece of code to check passwords for being obvious. This will detect any word in the UNIX dictionary, and most English words, using something that's vaguely like a Bloom filter.
This is so old it predates ANSI C; it's in K&R C. It used to show up on various academic sites. Now it's obsolete enough to have scrolled off Google.
I've seen copies of this on various academic sites over the years, but it seems to have finally scrolled off.
I think we can dispense with non 8-bit bytes at this point.
The tms320c28x DSPs have 16 bit char, so e.g. the Opus audio codec codebase works with 16-bit char (or at least it did at one point -- I wouldn't be shocked if it broke from time to time, since I don't think anyone runs regression tests on such a platform).
For some DSP-ish sort of processors I think it doesn't make sense to have addressability at char level, and the gates to support it would be better spent on better 16 and 32 bit multipliers. ::shrugs::
I feel kind of ambivalent about the standards proposal. We already have fixed size types. If you want/need an exact type, that already exists. The non-fixed size types set minimums and allow platforms to set larger sizes for performance reasons.
Having no fast 8-bit level access is a perfectly reasonable decision for a small DSP.
Might it be better instead to migrate many users of char to (u)int8_t?
The proposed alternative of CHAR_BIT congruent to 0 mod 8 also sounds pretty reasonable, in that it captures the existing non-8-bit char platforms and also the justification for non-8-bit char platforms (that if you're not doing much string processing but instead doing all math processing, the additional hardware for efficient 8 bit access is a total waste).
I thinks it's fine to relegate non 8 bit chars to non-standard C given that a lot of software anyway assumes 8bit bytes already implicitly. Non standard extensions for certain use-cases isn't anything new for C compilers. Also it's a C++ proposal I'm not sure if you program DSPs with C++ :think:
Ignoring this C++ proposal, especially because C and C++ seem like a complete nightmare when it comes to this stuff, I've almost gotten into the habit of treating a "byte" as a conceptual concept. Many serial protocols will often define a "byte", and it might be 7, 8, 9, 11, 12, or whatever bits long.
One fun fact I found the other day: ASCII is 7 bits, but when it was used with punch cards there was an 8th bit to make sure you didn't punch the wrong number of holes. https://rabbit.eng.miami.edu/info/ascii.html
A 9-bit byte is found on 36-bit machines in quarter-word mode.
Parity is for paper tape, not punched cards. Paper tape parity was never standardized. Nor was parity for 8-bit ASCII communications. Which is why there were devices with settings for EVEN, ODD, ZERO, and ONE for the 8th bit.
Punched cards have their very own encodings, only of historical interest.
>A 9-bit byte is found on 36-bit machines in quarter-word mode.
I've only programmed in high level programming languages in 8-bit-byte machines. I can't understand what you mean by this sentence.
So in a 36-bit CPU a word is 36 bits. And a byte isn't a word. But what is a word and how does it differ from a byte?
If you asked me what 32-bit/64-bit means in a CPU, I'd say it's how large memory addresses can be. Is that true for 36-bit CPUs or does it mean something else? If it's something else, then that means 64-bit isn't the "word" of a 64-bit CPU, so what would the word be?
the fact that this isn't already done after all these years is one of the reasons why I no longer use C/C++. it takes years and years to get anything done, even the tiniest, most obvious drama free changes. contrast with Go, which has had this since version 1, in 2012:
fgetc(3) and its companions always return character-by-character input as an int, and the reason is that EOF is represented as -1. An unsigned char is unable to represent EOF. If you're using the wrong return value, you'll never detect this condition.
However, if you don't receive an EOF, then it should be perfectly fine to cast the value to unsigned char without loss of precision.
Previously, in JF's "Can we acknowledge that every real computer works this way?" series: "Signed Integers are Two’s Complement" <https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p09...>
Maybe specifying that floats are always IEEE floats should be next? Though that would obsolete this Linux kernel classic so maybe not.
https://github.com/torvalds/linux/blob/master/include/math-e...
Whether double floats can silently have 80 bit accumulators is a controversial thing. Numerical analysis people like it. Computer science types seem not to because it's unpredictable. I lean towards, "we should have it, but it should be explicit", but this is not the most considered opinion. I think there's a legitimate reason why Intel included it in x87, and why DSPs include it.
That line is actually from a famous Dilbert cartoon.
I found this snapshot of it, though it's not on the real Dilbert site: https://www.reddit.com/r/linux/comments/73in9/computer_holy_...
This is the epitome, the climax, the crux, the ultimate, the holy grail, the crème de la crème of nerd sniping.
fuckin bravo
Love it
During an internship in 1986 I wrote C code for a machine with 10-bit bytes, the BBN C/70. It was a horrible experience, and the existence of the machine in the first place was due to a cosmic accident of the negative kind.
10-bit arithmetics are actually not uncommon on fpgas these days and are used in production in relatively modern applications.
10-bit C, however, ..........
How so? Arithmetic on FPGA usually use the minimum size that works, because any size over that will use more resources than needed.
9-bit bytes are pretty common in block RAM though, with the extra bit being used for either for ECC or user storage.
Somehow this machine found its way onto The Heart of Gold in a highly improbable chain of events.
I've worked on a machine with 9-bit bytes (and 81-bit instructions) and others with 6-bit ones - nether has a C compiler
I think the pdp-10 could have 9 bit bytes, depending on decisions you made in the compiler. I notice it's hard to Google information about this though. People say lots of confusing, conflicting things. When I google pdp-10 byte size it says a c++ compiler chose to represent char as 36 bits.
I programmed the Intel Intellivision cpu which had a 10 bit "decl". A wacky machine. It wasn't powerful enough for C.
D made a great leap forward with the following:
1. bytes are 8 bits
2. shorts are 16 bits
3. ints are 32 bits
4. longs are 64 bits
5. arithmetic is 2's complement
6. IEEE floating point
and a big chunk of wasted time trying to abstract these away and getting it wrong anyway was saved. Millions of people cried out in relief!
Oh, and Unicode was the character set. Not EBCDIC, RADIX-50, etc.
Yeah, this is something Java got right as well. It got "unsigned" wrong, but it got standardizing primitive bits correct
byte = 8 bits
short = 16
int = 32
long = 64
float = 32 bit IEEE
double = 64 bit IEEE
I like the Rust approach more: usize/isize are the native integer types, and with every other numeric type, you have to mention the size explicitly.
On the C++ side, I sometimes use an alias that contains the word "short" for 32-bit integers. When I use them, I'm explicitly assuming that the numbers are small enough to fit in a smaller than usual integer type, and that it's critical enough to performance that the assumption is worth making.
hindsight has its advantages
Yep. Pity about getting chars / string encoding wrong though. (Java chars are 16 bits).
But it’s not alone in that mistake. All the languages invented in that era made the same mistake. (C#, JavaScript, etc).
What's the right way?
UTF-8
When D was first implemented, circa 2000, it wasn't clear whether UTF-8, UTF-16, or UTF-32 was going to be the winner. So D supported all three.
utf8, for essentially the reasons mentioned in this manifesto: https://utf8everywhere.org/
"1. bytes are 8 bits"
How big is a bit?
This doesn't feel like a serious question, but in case this is still a mystery to you… the name bit is a portmanteau of binary digit, and as indicated by the word "binary", there are only two possible digits that can be used as values for a bit: 0 and 1.
> How big is a bit?
A quarter nybble.
A bit is either a 0 or 1. A byte is the smallest addressable piece of memory in your architecture.
Which … if your heap always returns N bit aligned values, for some N … is there a name for that? The smallest heap addressable segment?
Technically the smallest addressable piece of memory is a word.
Some people are still dealing with DSPs.
https://thephd.dev/conformance-should-mean-something-fputc-a...
Me? I just dabble with documenting an unimplemented "50% more bits per byte than the competition!" 12-bit fantasy console of my own invention - replete with inventions such as "UTF-12" - for shits and giggles.
They can just target C++23 or earlier, right? I have a small collection of SHARCs but I am not going to go crying to the committee if they make C++30 (or whatever) not support CHAR_BIT=32
no doubt you've got your brainfuck compiler hard at work on this ...
TI DSP Assembler is pretty high level, it's "almost C" already.
Writing geophysical | military signal and image processing applications on custom DSP clusters is suprisingly straightforward and doesn't need C++.
It's a RISC architecture optimised for DSP | FFT | Array processing with the basic simplification that char text is for hosts, integers and floats are at least 32 bit and 32 bits (or 64) is the smallest addressable unit.
Fantastic architecture to work with for numerics, deep computational pipelines, once "primed" you push in raw aquisition samples in chunks every clock cycle and extract processed moving window data chunks every clock cycle.
A single ASM instruction in a cycle can accumulate totals from vector multiplication and modulo update indexes on three vectors (two inputs and and out).
Not your mama's brainfuck.
Is C++ capable of deprecating or simplifying anything?
Honest question, haven't followed closely. rand() is broken,I;m told unfixable and last I heard still wasn't deprecated.
Is this proposal a test? "Can we even drop support for a solution to a problem literally nobody has?"
I think you are right. Absolutely.
Don’t break perfection!! Just accumulate more perfection.
What we need is a new C++ symbol that reliably references eight bit bytes, without breaking compatibility, or wasting anny opportunity to expand the kitchen sink once again.
I propose “unsigned byte8” and (2’s complement) “signed byte8”. And “byte8” with undefined sign behavior because we can always use some more spice.
“unsigned decimal byte8” and “signed decimal byte8”, would limit legal values to 0 to 10 and -10 to +10.
“unsigned centimal byte8” and “signed centimal byte8”, would limit legal values to 0 to 100 and -100 to +100.
And “float byte8” obviously.
Signed integers did not have to be 2’s complement, there were 3 valid representations: signed mag, 1s and 2s complement. Modern C and C++ dropped this and mandate 2s complement (“as if” but that distinction is moot here, you can do the same for CHAR_BIT). So there is certainly precedence for this sort of thing.
C++ long ago crossed the line where making any change is more work than any benefit it could ever create.
C++17 removed trigraphs
Which was quite controversial. Imagine that.
well they managed to get two's complement requirement into C++20. there is always hope.
Well then someone somewhere with some mainframe got so angry they decided to write a manifesto to condemn kids these days and announced a fork of Qt because Qt committed the cardinal sin of adopting C++20. So don’t say “a problem literally nobody has”, someone always has a use case; although at some point it’s okay to make a decision to ignore them.
https://lscs-software.com/LsCs-Manifesto.html
https://news.ycombinator.com/item?id=41614949
Edit: Fixed typo pointed out by child.
> because Qt committed the carnal sin of adopting C++20
I do believe you meant to write "cardinal sin," good sir. Unless Qt has not only become sentient but also corporeal when I wasn't looking and gotten close and personal with the C++ standard...
> We can find vestigial support, for example GCC dropped dsp16xx in 2004, and 1750a in 2002.
Honestly kind of surprised it was relavent as late as 2004. I thought the era of non 8-bit bytes was like 1970s or earlier.
This is both uncontroversial and incredibly spicy. I love it.
I'm totally fine with enforcing that int8_t == char == 8-bits, however I'm not sure about spreading the misconception that a byte is 8-bits. A byte with 8-bits is called an octet.
At the same time, a `byte` is already an "alias" for `char` since C++17 anyway[1].
[1] https://en.cppreference.com/w/cpp/types/byte
I, for one, hate that int8 == signed char.
std::cout << (int8_t)32 << std::endl; //should print 32 dang it
Now you can also enjoy the fact that you can't even compile:
because there is no default operator<< defined.Very enjoyable. It will a constant reminder that I need to decide how I want std::byte to print - character or integer ...
Hmm, I wonder if any modern languages can work on computers that use trits instead of bits.
https://en.wikipedia.org/wiki/Ternary_computer
Possible, but likely slow. There's nothing in the "C abstract machine" that mandates specific hardware. But, the bitshift is only a fast operation when you have bits. Similarly with bitwise boolean operations.
It'd just be a translation/compiler problem. Most languages don't really have a "bit", instead it's usually a byte with the upper bits ignored.
I just put static_assert(CHAR_BITS==8); in one place and move on. Haven't had it fire since it was #if equivalent
So please do excuse my ignorance, but is there a "logic" related reason other than hardware cost limitations ala "8 was cheaper than 10 for the same number of memory addresses" that bytes are 8 bits instead of 10? Genuinely curious, as a high-level dev of twenty years, I don't know why 8 was selected.
To my naive eye, It seems like moving to 10 bits per byte would be both logical and make learning the trade just a little bit easier?
One example from the software side: A common thing to do in data processing is to obtain bit offsets (compression, video decoding etc.). If a byte would be 10 bits you would need mod%10 operations everywhere which is slow and/or complex. In contrast mod%(2^N) is one logic processor instruction.
I'm fairly sure it's because the English character set fits nicely into a byte. 7 bits would have have worked as well, but 7 is a very odd width for something in a binary computer.
Eight is a nice power of two.
Can you explain how that's helpful? I'm not being obtuse, I just don't follow
One thought is that it's always a whole number of bits (3) to bit-address within a byte. It's 3.5 bits to bit address a 10 bit byte. Sorta just works out nicer in general to have powers of 2 when working on base 2.
This is basically the reason.
Another part of it is the fact that it's a lot easier to represent stuff with hex if the bytes line up.
I can represent "255" with "0xFF" which fits nice and neat in 1 byte. However, now if a byte is 10bits that hex no longer really works. You have 1024 values to represent. The max value would be 0x3FF which just looks funky.
Coming up with an alphanumeric system to represent 2^10 cleanly just ends up weird and unintuitive.
Many circuits have ceil(log_2(N_bits)) scaling wrt to propagation delay/other dimensions so you’re just leaving efficiency on the table if you aren’t using a power of 2 for your bit size.
It's easier to go from a bit number to (byte, bit) if you don't have to divide by 10.
Because modern computing has settled on the Boolean (binary) logic (0/1 or true/false) in the chip design, which has given us 8 bit bytes (a power of two). It is the easiest and most reliable to design and implement in the hardware.
On the other hand, if computing settled on a three-valued logic (e.g. 0/1/«something» where «something» has been proposed as -1, «undefined»/«unknown»/«undecided» or a «shade of grey»), we would have had 9 bit bytes (a power of three).
10 was tried numerous times at the dawn of computing and… it was found too unwieldy in the circuit design.
> On the other hand, if computing settled on a three-valued logic (e.g. 0/1/«something» where «something» has been proposed as -1, «undefined»/«unknown/undecided» or a «shade of grey»), we would have had 9 bit bytes (a power of three).
Is this true? 4 ternary bits give you really convenient base 12 which has a lot of desirable properties for things like multiplication and fixed point. Though I have no idea what ternary building blocks would look like so it’s hard to visualize potential hardware.
It is hard to say whether it would have been 9 or 12, now that people have stopped experimenting with alternative hardware designs. 9-bit byte designs certainly did exist (and maybe even the 12-bit designs), too, although they were still based on the Boolean logic.
I have certainly heard an argument that ternary logic would have been a better choice, if it won over, but it is history now, and we are left with the vestiges of the ternary logic in SQL (NULL values which are semantically «no value» / «undefined» values).
If you're ignoring what's efficient to use then just use a decimal data type and let the hardware figure out how to calculate that for you best. If what's efficient matters then address management, hardware operation implementations, and data packing are all simplest when the group size is a power of the base.
likely mostly as a concession to ASCII in the end. you used a typewriter to write into and receive terminal output from machines back in the day. terminals would use ASCII. there were machines with all sorts of smallest-addressable-sizes, but eight bit bytes align nicely with ASCII. makes strings easier. making strings easier makes programming easier. easier programming makes a machine more popular. once machines started standardizing on eight bit bytes, others followed. when they went to add more data, they kept the byte since code was written for bytes, and made their new registeres two bytes. then two of those. then two of those. so we're sitting at 64 bit registers on the backs of all that that came before.
I'm not sure why you think being able to store values from -512 to +511 is more logical than -128 to +127?
Buckets of 10 seem more regular to beings with 10 fingers that can be up or down?
I think 8bits (really 7 bits) was chosen because it holds a value closest to +/- 100. What is regular just depends on how you look at it.
Not sure about that, seems pretty controversial to me. Are we forgetting about the UNIVACs?
This would be a great setup for a time travelling science fiction where there is some legacy UNIVAC software that needs to be debugged, and John Titor, instead of looking for an IBM 5100, came back to the year 2024 to find a pre-P3477R0 compiler.
Hopefully we are; it's been a long time, but as I remember indexing in strings on them is a disaster.
They still exist. You can still run OS 2200 on a Clearpath Dorado.[1] Although it's actually Intel Xeon processors doing an emulation.
Yes, indexing strings of 6-bit FIELDATA characters was a huge headache. UNIVAC had the unfortunate problem of having to settle on a character code in the early 1960s, before ASCII was standardized. At the time, a military 6-bit character set looked like the next big thing. It was better than IBM's code, which mapped to punch card holes and the letters weren't all in one block.
[1] https://www.unisys.com/siteassets/collateral/info-sheets/inf...
idk. by today most software already assumes 8 bit == byte in subtle ways all over the place to a point you kinda have to use a fully custom or at least fully self reviewed and patched stack of C libraries
so delegating such by now very very edge cases to non standard C seems fine, i.e. seems to IMHO not change much at all in practice
and C/C++ compilers are anyway full of non standard extensions and it's not that CHAR_BIT go away or you as a non-standard extension assume it might not be 8
> most software already assumes 8 bit == byte in subtle ways all over the place
Which is the real reason why 8-bits should be adopted as the standard byte size.
I didn't even realize that the byte was defined as anything other than 8-bits until recently. I have known, for decades, that there were non-8-bit character encodings (including ASCII) and word sizes were all over the map (including some where word size % 8 != 0). Enough thought about that last point should have helped me realize that there were machines where the byte was not 8-bits, yet the rarity of encountering such systems left me with the incorrect notion that a byte was defined as 8-bits.
Now if someone with enough background to figure it out doesn't figure it out, how can someone without that background figure it out? Someone who has only experienced systems with 8-bit bytes. Someone who has only read books that make the explicit assumption of 8-bit bytes (which virtually every book does). Anything they write has the potential of breaking on systems with a different byte size. The idea of writing portable code because the compiler itself is "standards compliant" breaks down. You probably should modify the standard to ensure the code remains portable by either forcing the compiler for non-8-bit systems to handle the exceptions, or simply admitting that compiler does not portable code for non-8-bit systems.
Do UNIVACs care about modern C++ compilers? Do modern C++ compilers care about UNIVACs?
Given that Wikipedia says UNIVAC was discontinued in 1986 I’m pretty sure the answer is no and no!
The UNIVAC 1108 (and descendants) mainframe architecture was not discontinued in 1986. The company that owned it (Sperry) merged with Burroughs in that year to form Unisys. The platform still exists, but now runs as a software emulator under x86-64. The OS is still maintained and had a new release just last year. Around the time of the merger the old school name “UNIVAC” was retired in a rebranding, but the platform survived.
Its OS, OS 2200, does have a C compiler. Not sure if there ever was a C++ compiler, if there once was it is no longer around. But that C compiler is not being kept up to date with the latest standards, it only officially supports C89/C90 - this is a deeply legacy system, most application software is written in COBOL and the OS itself itself is mainly written in assembler and a proprietary Pascal-like language called “PLUS”. They might add some features from newer standards if particularly valuable, but formal compliance with C99/C11/C17/C23/etc is not a goal.
The OS does contain components written in C++, most notably the HotSpot JVM. However, from what I understand, the JVM actually runs in x86-64 Linux processes on the host system, outside of the emulated mainframe environment, but the mainframe emulator is integrated with those Linux processes so they can access mainframe files/data/apps.
But how many bytes are there in a word?
If you're on x86, the answer can be simultaneously 16, 32, and 64.
"Word" is an outdated concept we should try to get rid of.
You're right. To be consistent with bytes we should call it a snack.
Henceforth, it follows that a doublesnack is called a lunch. And a quadruplesnack a fourthmeal.
There's only one right answer:
Nybble - 4 bits
Byte - 8 bits
Snyack - 16 bits
Lyunch - 32 bits
Dynner - 64 bits
And what about elevensies?
(Ok,. I guess there's a difference between bits and hob-bits)
or an f-word
It's very useful on hardware that is not an x86 CPU.
As an abstraction on the size of a CPU register, it really turned out to be more confusing than useful.
On RISC machines, it can be very useful to have the concept of "words," because that indicates things about how the computer loads and stores data, as well as the native instruction size. In DSPs and custom hardware, it can indicate the only available datatype.
The land of x86 goes to great pains to eliminate the concept of a word at a silicon cost.
Fortunately we have `register_t` these days.
Is it 32 or 64 bits on ARM64? Why not both?
such as...?
How exactly ? How else do you suggest CPUs do addressing ?
Or are you suggesting to increase the size of a byte until it's the same size as a word, and merge both concepts ?
I'm saying the term "Word" abstracting the number of bytes a CPU can process in a single operation is an outdated concept. We don't really talk about word-sized values anymore. Instead we mostly explicit on the size of value in bits. Even the idea of a CPU having just one relevant word size is a bit outdated.
There are 4 bytes in word:
I've seen 6 8-bit characters/word (Burroughs large systems, they also support 8 6-bit characters/word)
And then we lose communication with Europa Clipper.
How many bytes is a devour?
This is entertaining and probably a good idea but the justification is very abstract.
Specifically, has there even been a C++ compiler on a system where bytes weren't 8 bits? If so, when was it last updated?
There were/are C++ compilers for PDP-10 (9 bit byte). Those haven't been maintained AFAICT, but there are C++ compilers for various DSP's where the smallest unit of access is 16 or 32 bits that are still being sold.
I know some DSPs have 24-bit "bytes", and there are C compilers available for them.
Hoesntly at thought this might be an onion headline. But then I stopped to think about it.
Why? Pls no. We've been told (in school!) that byte is byte. Its only sometimes 8bits long (ok, most of the time these days). Do not destroy the last bits of fun. Is network order little endian too?
Heretic, do not defile the last remnants of true order!
I think there's plenty of fun left in the standard if they remove this :)
As a person who designed and built a hobby CPU with a sixteen-bit byte, I’m not sure how I feel about this proposal.
Amazing stuff guys. Bravo.
There are FOUR bits.
Jean-Luc Picard
Bold leadership
Incredible things are happening in the C++ community.
But think of ternary computers!
Doesn't matter ternary computers just have ternary bits, 8 of them ;)
Ternary computers have 8 tits to a byte.
Should be either 9 or 27 I'd think.
Why can’t it be 8?, the fact that it’s a trit doesn’t put any constraint on the byte (tryte ? size). You could actually make it 5 or 6 trits (~9.5 bits) for similar information density. The Setun used 6 trit addressable units.
Supposedly, "bit" is short for "binary digit", so we'd need a separate term for "ternary digit", but I don't wanna go there.
The prefix is tri-, not ti- so I don’t think there was any concern of going anywhere.
It’s tricycle and tripod, not ticycle.
The standard term is "trit" because they didn't want to go there.
JF Bastien is a legend for this, haha.
I would be amazed if there's any even remotely relevant code that deals meaningfully with CHAR_BIT != 8 these days.
(... and yes, it's about time.)
Here's a bit of 40 year old code I wrote which originally ran on 36-bit PDP-10 machines, but will work on non-36 bit machines.[1] It's a self-contained piece of code to check passwords for being obvious. This will detect any word in the UNIX dictionary, and most English words, using something that's vaguely like a Bloom filter.
This is so old it predates ANSI C; it's in K&R C. It used to show up on various academic sites. Now it's obsolete enough to have scrolled off Google. I've seen copies of this on various academic sites over the years, but it seems to have finally scrolled off.
I think we can dispense with non 8-bit bytes at this point.
[1] https://animats.com/source/obvious/obvious.c
DSP chips are a common exception that people bring up. I think some TI made ones have 64 bit chars.
Edit: I see TFA mentions them but questions how relevant C++ is in that sort of embedded environment.
Yes, but you're already in specialized territory if you're using that
The tms320c28x DSPs have 16 bit char, so e.g. the Opus audio codec codebase works with 16-bit char (or at least it did at one point -- I wouldn't be shocked if it broke from time to time, since I don't think anyone runs regression tests on such a platform).
For some DSP-ish sort of processors I think it doesn't make sense to have addressability at char level, and the gates to support it would be better spent on better 16 and 32 bit multipliers. ::shrugs::
I feel kind of ambivalent about the standards proposal. We already have fixed size types. If you want/need an exact type, that already exists. The non-fixed size types set minimums and allow platforms to set larger sizes for performance reasons.
Having no fast 8-bit level access is a perfectly reasonable decision for a small DSP.
Might it be better instead to migrate many users of char to (u)int8_t?
The proposed alternative of CHAR_BIT congruent to 0 mod 8 also sounds pretty reasonable, in that it captures the existing non-8-bit char platforms and also the justification for non-8-bit char platforms (that if you're not doing much string processing but instead doing all math processing, the additional hardware for efficient 8 bit access is a total waste).
I thinks it's fine to relegate non 8 bit chars to non-standard C given that a lot of software anyway assumes 8bit bytes already implicitly. Non standard extensions for certain use-cases isn't anything new for C compilers. Also it's a C++ proposal I'm not sure if you program DSPs with C++ :think:
Ignoring this C++ proposal, especially because C and C++ seem like a complete nightmare when it comes to this stuff, I've almost gotten into the habit of treating a "byte" as a conceptual concept. Many serial protocols will often define a "byte", and it might be 7, 8, 9, 11, 12, or whatever bits long.
I wish I knew what a 9 bit byte means.
One fun fact I found the other day: ASCII is 7 bits, but when it was used with punch cards there was an 8th bit to make sure you didn't punch the wrong number of holes. https://rabbit.eng.miami.edu/info/ascii.html
A 9-bit byte is found on 36-bit machines in quarter-word mode.
Parity is for paper tape, not punched cards. Paper tape parity was never standardized. Nor was parity for 8-bit ASCII communications. Which is why there were devices with settings for EVEN, ODD, ZERO, and ONE for the 8th bit.
Punched cards have their very own encodings, only of historical interest.
>A 9-bit byte is found on 36-bit machines in quarter-word mode.
I've only programmed in high level programming languages in 8-bit-byte machines. I can't understand what you mean by this sentence.
So in a 36-bit CPU a word is 36 bits. And a byte isn't a word. But what is a word and how does it differ from a byte?
If you asked me what 32-bit/64-bit means in a CPU, I'd say it's how large memory addresses can be. Is that true for 36-bit CPUs or does it mean something else? If it's something else, then that means 64-bit isn't the "word" of a 64-bit CPU, so what would the word be?
This is all very confusing.
Obviously
the fact that this isn't already done after all these years is one of the reasons why I no longer use C/C++. it takes years and years to get anything done, even the tiniest, most obvious drama free changes. contrast with Go, which has had this since version 1, in 2012:
https://pkg.go.dev/builtin@go1#byte
In a char, not in a byte. Byte != char
Nope: https://isocpp.org/wiki/faq/intrinsic-types#bytes-review
A common programming error in C is reading input as char rather than int.
https://man7.org/linux/man-pages/man3/fgetc.3.html
fgetc(3) and its companions always return character-by-character input as an int, and the reason is that EOF is represented as -1. An unsigned char is unable to represent EOF. If you're using the wrong return value, you'll never detect this condition.
However, if you don't receive an EOF, then it should be perfectly fine to cast the value to unsigned char without loss of precision.