diff options
Diffstat (limited to 'src/math/cosh.c')
| -rw-r--r-- | src/math/cosh.c | 41 |
1 files changed, 19 insertions, 22 deletions
diff --git a/src/math/cosh.c b/src/math/cosh.c index a1f7dbc7..2fcdea8f 100644 --- a/src/math/cosh.c +++ b/src/math/cosh.c @@ -23,7 +23,7 @@ * 2 * 22 <= x <= lnovft : cosh(x) := exp(x)/2 * lnovft <= x <= ln2ovft: cosh(x) := exp(x/2)/2 * exp(x/2) - * ln2ovft < x : cosh(x) := huge*huge (overflow) + * ln2ovft < x : cosh(x) := inf (overflow) * * Special cases: * cosh(x) is |x| if x is +INF, -INF, or NaN. @@ -32,43 +32,40 @@ #include "libm.h" -static const double huge = 1.0e300; - double cosh(double x) { - double t, w; - int32_t ix; - - GET_HIGH_WORD(ix, x); - ix &= 0x7fffffff; + union {double f; uint64_t i;} u = {.f = x}; + uint32_t ix; + double t; - /* x is INF or NaN */ - if (ix >= 0x7ff00000) - return x*x; + /* |x| */ + u.i &= (uint64_t)-1/2; + x = u.f; + ix = u.i >> 32; /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */ if (ix < 0x3fd62e43) { - t = expm1(fabs(x)); - w = 1.0+t; + t = expm1(x); if (ix < 0x3c800000) - return w; /* cosh(tiny) = 1 */ - return 1.0 + (t*t)/(w+w); + return 1; + return 1 + t*t/(2*(1+t)); } /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|))/2; */ if (ix < 0x40360000) { - t = exp(fabs(x)); + t = exp(x); return 0.5*t + 0.5/t; } /* |x| in [22, log(maxdouble)] return 0.5*exp(|x|) */ - if (ix < 0x40862E42) - return 0.5*exp(fabs(x)); + if (ix < 0x40862e42) + return 0.5*exp(x); /* |x| in [log(maxdouble), overflowthresold] */ - if (ix <= 0x408633CE) - return __expo2(fabs(x)); + if (ix <= 0x408633ce) + return __expo2(x); - /* |x| > overflowthresold, cosh(x) overflow */ - return huge*huge; + /* overflow (or nan) */ + x *= 0x1p1023; + return x; } |