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Work around a glibc bug where it truncates the argument to fpclassify()
from double to float by implementing fpclassify() ourselves.
Correctness test (Note that the FP_SUBNORMAL test depends on an atof() that
knows how to parse subnormals. Glibc does, not sure about other libcs.):
#include <math.h>
#include <stdint.h>
#include <string.h>
int xfpclassify(double d)
{
uint64_t m;
int e;
memcpy(&m, &d, sizeof(m));
e = 0x7ff & (m >> 52);
m = 0xfffffffffffffULL & m;
switch (e) {
default: return FP_NORMAL;
case 0x000: return m ? FP_SUBNORMAL : FP_ZERO;
case 0x7ff: return m ? FP_NAN : FP_INFINITE;
}
}
#include <assert.h>
#include <stdlib.h>
int main(void)
{
assert(FP_ZERO == xfpclassify(atof("0.0")));
assert(FP_ZERO == xfpclassify(atof("-0.0")));
assert(FP_NORMAL == xfpclassify(atof("1.0")));
assert(FP_NORMAL == xfpclassify(atof("-1.0")));
assert(FP_INFINITE == xfpclassify(atof("inf")));
assert(FP_INFINITE == xfpclassify(atof("-inf")));
assert(FP_NAN == xfpclassify(atof("nan")));
assert(FP_NAN == xfpclassify(atof("-nan")));
assert(FP_SUBNORMAL == xfpclassify(atof("1.8011670033376514e-308")));
return 0;
}
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