3 ms·
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-1
by larsbrinkhoff 2y ago
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.
- eqvinox 2y agoDo 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
- larsbrinkhoff 2y agoIt should be in the description for the byte instructions: LDB, DPB, IBP, and ILDB. http://bitsavers.org/pdf/dec/pdp10/1970_PDP-10_Ref/ 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.
- asveikau 2y agoI was summarizing this from a Google search. https://isocpp.org/wiki/faq/intrinsic-types#:~:text=One%20way%20to%20abide%20by,bit%2Doffset%20within%20that%20word https://isocpp.org/wiki/faq/intrinsic-types#:~:text=One%20wa.... As I read it, this link may be describing a hypothetical rather than real compiler. But I did not parse that on initial scan of the Google result.