On 3/28/20 8:17 AM, LIU Zhiwei wrote: >> Missed the improvement here. See tcg_gen_mulsu2_i64. > Though I have not gotten the principle, the code in tcg_gen_mulsu2_i64 is much > tidier.
Let A = signed operand,
B = unsigned operand
P = unsigned product
If the sign bit A is set, then P is too large.
In that case we subtract 2**64 * B to fix that:
HI_P -= (A < 0 ? B : 0)
where the conditional is computed as (A >> 63) & B.
r~
