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math: fix fma(x,y,0) when x*y rounds to -0

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if x!=0, y!=0, z==0 then

  fma(x,y,z) == x*y

in all rounding modes, while adding z can ruin the sign of 0 if x*y
rounds to -0.
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Szabolcs Nagy 2024-04-23 09:21:08 -07:00 • committed by Justine Tunney
parent 01267ea0f5
commit ea3cc4ea0b
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libc/tinymath/fma.c
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@ -145,7 +145,7 @@ double fma(double x, double y, double z)
return x*y + z; return x*y + z;
if (nz.e >= ZEROINFNAN) { if (nz.e >= ZEROINFNAN) {
if (nz.e > ZEROINFNAN) /* z==0 */ if (nz.e > ZEROINFNAN) /* z==0 */
return x*y + z; return x*y;
return z; return z;
} }