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C++ proposal: There are exactly 8 bits in a byte

(www.open-std.org)
288 points Twirrim | 2 comments | 17 Oct 24 22:21 UTC | HN request time: 0.682s | source
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pjdesno ◴[17 Oct 24 23:31 UTC] No.41874875[source]▶
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.
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Taniwha ◴[18 Oct 24 00:32 UTC] No.41875248[source]▶
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
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asveikau ◴[18 Oct 24 01:46 UTC] No.41875661[source]▶
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.
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larsbrinkhoff ◴[18 Oct 24 06:30 UTC] No.41876849[source]▶
PDP-10 byte size is not fixed. Bytes can be 0 to 36 bits wide. (Sure, 0 is not very useful; still legal.)

I don't think there is a C++ compiler for the PDP-10. One of the C compiler does have a 36-bit char type.

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1. eqvinox ◴[18 Oct 24 10:04 UTC] No.41877850[source]▶
Do you have any links/info on how that 0-bit byte worked? It sounds like just the right thing for a Friday afternoon read ;D
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2. larsbrinkhoff ◴[18 Oct 24 11:04 UTC] No.41878248[source]▶
It should be in the description for the byte instructions: LDB, DPB, IBP, and ILDB. http://bitsavers.org/pdf/dec/pdp10/1970_PDP-10_Ref/

Basically, loading a 0-bit byte from memory gets you a 0. Depositing a 0-bit byte will not alter memory, but may do an ineffective read-modify-write cycle. Incrementing a 0-bit byte pointer will leave it unchanged.