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0 pointsflohofwoe1y ago0 comments

Signed and unsigned are just different views on the same bits. CPU registers don't carry signedness either after all, the value they carry is neither signed nor unsigned until you look at the bits and decide to "view" them as a signed or unsigned number.

With the two's complement convention, the concept of 'signedness' only matters when a narrow integer value needs to be extended to a wider value (e.g. 8-bit to 16-bit), specifically whether the new bits needs to be replicated from the narrow value's topmost bit (for signed extension) or set to zero (for unsigned extension).

It would be interesting to speculate what a high level language would look like with such sign-agnostic "Schroedinger's integer types").

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jeberle1y ago

CPU instruction sets do account for signed vs unsigned integers. SHR vs SAR for example. It's part of the ISAs. I'm calling this out as AFAIK, the JVM has no support for unsigned ints and so that in turn makes WASM a little more compelling.

https://en.wikibooks.org/wiki/X86_Assembly/Shift_and_Rotate

flohofwoeOP1y ago

Yes some instructions do - but surprisingly few (for instance there's signed/unsigned mul/div instructions, but add/sub are 'sign-agnostic'). The important part is that any 'signedness' is associated with the operation, and not with the operands or results.

kaba01y ago

Well, it has compiler intrinsics for unsigned numbers, for what it’s worth.

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