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00646ca204
scalbn() implementation from libm. (The two functions are defined to
be identical, but ldexp() lives in libc for backwards compatibility.)
The old ldexp() implementation...
- was more complicated than this one
- set errno instead of raising FP exceptions
- got some corner cases wrong
(e.g. ldexp(1.0, 2000) in round-to-zero mode)
The new implementation lives in libc/gen instead of
libc/$MACHINE_ARCH/gen, since we don't need N copies of a
machine-independent file. The amd64 and i386 platforms
retain their fast and correct MD implementations and
override this one.
124 lines
2.9 KiB
C
124 lines
2.9 KiB
C
/* @(#)s_scalbn.c 5.1 93/09/24 */
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/* @(#)fdlibm.h 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <machine/endian.h>
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#include <math.h>
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/* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
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#if BYTE_ORDER == BIG_ENDIAN
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typedef union
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{
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double value;
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struct
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{
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u_int32_t msw;
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u_int32_t lsw;
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} parts;
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} ieee_double_shape_type;
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#endif
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#if BYTE_ORDER == LITTLE_ENDIAN
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typedef union
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{
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double value;
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struct
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{
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u_int32_t lsw;
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u_int32_t msw;
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} parts;
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} ieee_double_shape_type;
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#endif
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/* Get two 32 bit ints from a double. */
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#define EXTRACT_WORDS(ix0,ix1,d) \
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do { \
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ieee_double_shape_type ew_u; \
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ew_u.value = (d); \
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(ix0) = ew_u.parts.msw; \
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(ix1) = ew_u.parts.lsw; \
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} while (0)
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/* Get the more significant 32 bit int from a double. */
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#define GET_HIGH_WORD(i,d) \
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do { \
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ieee_double_shape_type gh_u; \
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gh_u.value = (d); \
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(i) = gh_u.parts.msw; \
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} while (0)
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/* Set the more significant 32 bits of a double from an int. */
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#define SET_HIGH_WORD(d,v) \
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do { \
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ieee_double_shape_type sh_u; \
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sh_u.value = (d); \
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sh_u.parts.msw = (v); \
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(d) = sh_u.value; \
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} while (0)
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static const double
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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huge = 1.0e+300,
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tiny = 1.0e-300;
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static double
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_copysign(double x, double y)
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{
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u_int32_t hx,hy;
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GET_HIGH_WORD(hx,x);
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GET_HIGH_WORD(hy,y);
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SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
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return x;
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}
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double
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ldexp(double x, int n)
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{
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int32_t k,hx,lx;
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EXTRACT_WORDS(hx,lx,x);
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k = (hx&0x7ff00000)>>20; /* extract exponent */
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if (k==0) { /* 0 or subnormal x */
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if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
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x *= two54;
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GET_HIGH_WORD(hx,x);
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k = ((hx&0x7ff00000)>>20) - 54;
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if (n< -50000) return tiny*x; /*underflow*/
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}
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if (k==0x7ff) return x+x; /* NaN or Inf */
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k = k+n;
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if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */
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if (k > 0) /* normal result */
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{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
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if (k <= -54) {
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if (n > 50000) /* in case integer overflow in n+k */
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return huge*_copysign(huge,x); /*overflow*/
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else return tiny*_copysign(tiny,x); /*underflow*/
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}
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k += 54; /* subnormal result */
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SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
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return x*twom54;
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}
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