On 11/04/2015 11:45 AM, Paolo Bonzini wrote:
int32_t src = rs2 >> (word * 32);
- int64_t scaled = src << scale;
+ int64_t scaled = (int64_t)src << scale;
int64_t from_fixed = scaled >> 16;
...
I do think we'd be better served by casting to uint64_t on that line.
Note that fpackfix requires the same correction. And it wouldn't hurt
to cast to uint32_t in fpack16, lest we anger the self-same shifting gods.
Hmmm.. say src = -0x80000000, scale = 1;
scaled = (uint64_t)-0x8000000 << 1 = 0xffffffff00000000
from_fixed = 0xffffffff00000000 >> 16 = 0x0000ffffffff0000
Now from_fixed is positive and you get 32767 instead of -32768. In
other words, we would have to cast to uint64_t on the scaled assignment,
and back to int64_t on the from_fixed assignment. I must be
misunderstanding your suggestion.
int64_t scaled = (uint64_t)src << scale;
I.e. one explicit conversion and one implicit conversion.
r~
