Szabolcs Nagy
98be442ee8
use -1/(x*x) instead of -1/(x+0) to return -inf, -0+0 is -0 in downward rounding mode
18 lines
228 B
C
18 lines
228 B
C
#include <math.h>
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/*
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special cases:
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logb(+-0) = -inf, and raise divbyzero
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logb(+-inf) = +inf
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logb(nan) = nan
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*/
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double logb(double x)
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{
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if (!isfinite(x))
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return x * x;
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if (x == 0)
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return -1/(x*x);
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return ilogb(x);
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}
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