diff options
Diffstat (limited to 'src/math/exp.c')
| -rw-r--r-- | src/math/exp.c | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/src/math/exp.c b/src/math/exp.c index 5c0edee4..5ec8f8a7 100644 --- a/src/math/exp.c +++ b/src/math/exp.c @@ -80,7 +80,7 @@ P5 = 4.13813679705723846039e-08; /* 0x3E663769, 0x72BEA4D0 */ double exp(double x) { - double hi, lo, c, z; + double hi, lo, c, xx; int k, sign; uint32_t hx; @@ -92,24 +92,26 @@ double exp(double x) if (hx >= 0x40862e42) { /* if |x| >= 709.78... */ if (isnan(x)) return x; + if (hx == 0x7ff00000 && sign) /* -inf */ + return 0; if (x > 709.782712893383973096) { /* overflow if x!=inf */ STRICT_ASSIGN(double, x, 0x1p1023 * x); return x; } if (x < -745.13321910194110842) { - /* underflow if x!=-inf */ - STRICT_ASSIGN(double, x, 0x1p-1000 / -x * 0x1p-1000); + /* underflow */ + STRICT_ASSIGN(double, x, 0x1p-1000 * 0x1p-1000); return x; } } /* argument reduction */ if (hx > 0x3fd62e42) { /* if |x| > 0.5 ln2 */ - if (hx < 0x3ff0a2b2) /* if |x| < 1.5 ln2 */ - k = 1 - sign - sign; /* optimization */ - else + if (hx >= 0x3ff0a2b2) /* if |x| >= 1.5 ln2 */ k = (int)(invln2*x + half[sign]); + else + k = 1 - sign - sign; hi = x - k*ln2hi; /* k*ln2hi is exact here */ lo = k*ln2lo; STRICT_ASSIGN(double, x, hi - lo); @@ -124,9 +126,9 @@ double exp(double x) } /* x is now in primary range */ - z = x*x; - c = x - z*(P1+z*(P2+z*(P3+z*(P4+z*P5)))); - x = 1 + ((x*c/(2-c) - lo) + hi); + xx = x*x; + c = x - xx*(P1+xx*(P2+xx*(P3+xx*(P4+xx*P5)))); + x = 1 + (x*c/(2-c) - lo + hi); if (k == 0) return x; return scalbn(x, k); |