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~

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