[lgammaf] fix non-portability in the computation of signgam
The k>>31
in signgam = 1 - (((k&(k>>31))&1)<<1);
is not portable:
- The ISO C standard says "If E1 has a signed type and a negative value, the resulting value is implementation-defined." (this is still in C23).
- If the int type is larger than 32 bits (e.g. a 64-bit type),
then
k = INT_MAX;
line 144 will makek>>31
put 1 in bit 0 (thussigngam
will be -1) while 0 is expected.
Moreover, instead of the fx >= 0x1p31f
condition, testing fx >= 0
is probably better for 2 reasons:
- The
signgam
expression has more or less a condition on the sign offx
(the goal ofk>>31
, which can be dropped with this new condition). Since fx ≥ 0 should be the most common case, one can get signgam directly in this case (value 1). And this simplifies the expression for the other case (fx < 0). - This new condition may be easier/faster to test on the processor (e.g. by avoiding a load of a constant from the memory).