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Handle NaN and Inf edge cases as specified by posix, instead of barfing.

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We're not a posix system, but the posix spec is a good reference
	for what we should do.

	Thanks Geoff for the inspiration for this patch.
This commit is contained in:
Ori Bernstein 2019-06-16 15:55:55 -07:00
parent 55f018df8a
commit 37a5e86bf0
1 changed files with 47 additions and 1 deletions
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48
sys/src/libc/port/pow.c
View file

@ -1,6 +1,16 @@
#include <u.h>
#include <libc.h>
static int
isodd(double v)
{
double iv;
if(modf(v, &iv) != 0)
return 0;
return (vlong)iv & 1;
}
double
pow(double x, double y) /* return x ^ y (exponentiation) */
{
@ -8,8 +18,44 @@ pow(double x, double y) /* return x ^ y (exponentiation) */
long i;
int ex, ey, flip;
if(y == 0.0)
/*
* Special cases.
* Checking early here prevents an infinite loop.
* We need to test if !isNaN() here because otherwise
* we trap.
*/
if(!isNaN(x) && x == 1.0)
return 1.0;
if(!isNaN(y) && y == 0.0)
return 1.0;
if(isNaN(x) || isNaN(y))
return NaN();
if(isInf(x, 1)){
if(y < 0)
return 0.0;
else
return Inf(1);
}else if(isInf(x, -1)){
if(y < 0)
return isodd(y) ? -0.0 : 0.0;
else if(y > 0)
return isodd(y) ? Inf(-1) : Inf(1);
}
if(isInf(y, 1)){
if(x == -1.0)
return 1.0;
else if(fabs(x) < 1.0)
return 0.0;
else if(fabs(x) > 1.0)
return Inf(1);
}else if(isInf(y, -1)){
if(x == -1.0)
return 1.0;
else if(fabs(x) < 1.0)
return Inf(1);
else if(fabs(x) > 1.0)
return 0.0;
}
flip = 0;
if(y < 0.){