On 9/4/21 10:35 PM, Philipp Tomsich wrote:
Assume clzw being executed on a register that is not sign-extended, such
as for the following sequence that uses (1ULL << 63) | 392 as the operand
to clzw:
bseti a2, zero, 63
addi a2, a2, 392
clzw a3, a2
The correct result of clzw would be 23, but the current implementation
returns -32 (as it performs a 64bit clz, which results in 0 leading zero
bits, and then subtracts 32).
Fix this by changing the implementation to:
1. shift the original register up by 32
2. performs a target-length (64bit) clz
3. return 32 if no bits are set
Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
---
Changes in v10:
- New patch, fixing correctnes for clzw called on a register with undefined
(as in: not properly sign-extended) upper bits.
But we have
return gen_unary(ctx, a, EXT_ZERO, gen_clzw);
should *not* be undefined. Ah, what's missing is
ctx->w = true;
within trans_clzw to cause the extend to take effect.
There are a few other "w" functions that are missing that set, though they use EXT_NONE so
there is no visible bug, it would probably be best to set w anyway.
r~
