Failed to encode comparison immediate

[abrown]

@markcharney, I think I found an issue where xed-asmparse-main fails to encode the instruction when the immediate is 0:

$ xed-asmparse-main 'cmpps xmm7, xmm15, 0'
Forcing mode to 64b based on regs used
Guessing 32b EOSZ
MODE=64, EOSZ=32
ERROR: Failed to encode input: GENERAL_ERROR

$ xed-asmparse-main 'cmpps xmm7, xmm15, 1'
Forcing mode to 64b based on regs used
Guessing 32b EOSZ
MODE=64, EOSZ=32
Result: 41 0f c2 ff 01

I wouldn't expect that first one to fail, but maybe I'm doing something wrong?

[markcharney]

I looked. Use 00 instead of 0 and it'll work fine.

This is a little quirk of the parser for numbers that begin with 0's. For numbers that begin with zero's it assumes hex and it assumes someone was trying to specify some explicit hex value with a specific width. So it sees 0, one nibble, so 4 bits. And then the encoder says there is no such cmpps with a 4b immediate, which is technically true. Possibly I should change this. I'll think about it.

For values that do not begin with 0, it just gives 1/2/4/8 bytes (mutiplied by 8 for bits) depending on the actual numerical value.

[abrown]

Ah, I see. I would have expected 0x... to parse as hex values and un-prefixed numerics to parse as decimal values.

For values that do not begin with 0, it just gives 1/2/4/8 bytes (mutiplied by 8 for bits) depending on the actual numerical value.

To make sure I understand, un-prefixed numerics are parsed as decimals?