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Diffstat (limited to 'lib/msun/src/e_log2f.c')
-rw-r--r-- | lib/msun/src/e_log2f.c | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/lib/msun/src/e_log2f.c b/lib/msun/src/e_log2f.c new file mode 100644 index 0000000..7166346 --- /dev/null +++ b/lib/msun/src/e_log2f.c @@ -0,0 +1,81 @@ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunPro, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +/* + * Float version of e_log2.c. See the latter for most comments. + */ + +#include "math.h" +#include "math_private.h" +#include "k_logf.h" + +static const float +two25 = 3.3554432000e+07, /* 0x4c000000 */ +ivln2hi = 1.4428710938e+00, /* 0x3fb8b000 */ +ivln2lo = -1.7605285393e-04; /* 0xb9389ad4 */ + +static const float zero = 0.0; + +float +__ieee754_log2f(float x) +{ + float f,hfsq,hi,lo,r,y; + int32_t i,k,hx; + + GET_FLOAT_WORD(hx,x); + + k=0; + if (hx < 0x00800000) { /* x < 2**-126 */ + if ((hx&0x7fffffff)==0) + return -two25/zero; /* log(+-0)=-inf */ + if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ + k -= 25; x *= two25; /* subnormal number, scale up x */ + GET_FLOAT_WORD(hx,x); + } + if (hx >= 0x7f800000) return x+x; + if (hx == 0x3f800000) + return zero; /* log(1) = +0 */ + k += (hx>>23)-127; + hx &= 0x007fffff; + i = (hx+(0x4afb0d))&0x800000; + SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */ + k += (i>>23); + y = (float)k; + f = x - (float)1.0; + hfsq = (float)0.5*f*f; + r = k_log1pf(f); + + /* + * We no longer need to avoid falling into the multi-precision + * calculations due to compiler bugs breaking Dekker's theorem. + * Keep avoiding this as an optimization. See e_log2.c for more + * details (some details are here only because the optimization + * is not yet available in double precision). + * + * Another compiler bug turned up. With gcc on i386, + * (ivln2lo + ivln2hi) would be evaluated in float precision + * despite runtime evaluations using double precision. So we + * must cast one of its terms to float_t. This makes the whole + * expression have type float_t, so return is forced to waste + * time clobbering its extra precision. + */ + if (sizeof(float_t) > sizeof(float)) + return (r - hfsq + f) * ((float_t)ivln2lo + ivln2hi) + y; + + hi = f - hfsq; + GET_FLOAT_WORD(hx,hi); + SET_FLOAT_WORD(hi,hx&0xfffff000); + lo = (f - hi) - hfsq + r; + return (lo+hi)*ivln2lo + lo*ivln2hi + hi*ivln2hi + y; +} |