3 ms·

Thx for this perspective and info. Regarding "signedness and floating point that closer matches hardware", I'm not seeing unsigned integers. Are they supported?

Thx for this perspective and info. Regarding "signedness and floating point that closer matches hardware", I'm not seeing unsigned integers. Are they supported? I see only: > Two’s complement signed integers in 32 bits and optionally 64 bits. https://webassembly.org/docs/portability/#assumptions-for-efficient-execution https://webassembly.org/docs/portability/#assumptions-for-ef... And nothing suggesting unsigned ints here: https://webassembly.org/features/ https://webassembly.org/features/

Laremere 2y ago
Wasm makes no distinction between signed and unsigned integers as variables, only calling them integers. The relevant operations are split between signed and unsigned. https://webassembly.github.io/spec/core/appendix/index-instructions.html https://webassembly.github.io/spec/core/appendix/index-instr... See how there's only i32.load and i32.eq, but there's i32.lt_u and i32.lt_s. Loading bits from memory or comparing them is the same operation bit for bit for each of signed and unsigned. However, less than requires knowing the desired signess, and is split between signed and unsigned.
flohofwoe 2y ago
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").
- jeberle 2y 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 https://en.wikibooks.org/wiki/X86_Assembly/Shift_and_Rotate
  - kaba0 2y ago
    Well, it has compiler intrinsics for unsigned numbers, for what it’s worth.
  - flohofwoe 2y 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.

Laremere 2y ago

Wasm makes no distinction between signed and unsigned integers as variables, only calling them integers. The relevant operations are split between signed and unsigned. https://webassembly.github.io/spec/core/appendix/index-instructions.html https://webassembly.github.io/spec/core/appendix/index-instr... See how there's only i32.load and i32.eq, but there's i32.lt_u and i32.lt_s. Loading bits from memory or comparing them is the same operation bit for bit for each of signed and unsigned. However, less than requires knowing the desired signess, and is split between signed and unsigned.

flohofwoe 2y ago

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").

jeberle 2y 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 https://en.wikibooks.org/wiki/X86_Assembly/Shift_and_Rotate
- kaba0 2y ago
  Well, it has compiler intrinsics for unsigned numbers, for what it’s worth.
- flohofwoe 2y 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.