mirror of git://git.musl-libc.org/musl
simplify scalbn*.c implementations
The old scalbn.c was wrong and slow, the new one is just slow. (scalbn(0x1p+1023,-2097) should give 0x1p-1074, but the old code gave 0)
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nsz
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f767aba8af
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8051e08e10
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@ -1,62 +1,28 @@
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/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbn.c */
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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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/*
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* scalbn (double x, int n)
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* scalbn(x,n) returns x* 2**n computed by exponent
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* manipulation rather than by actually performing an
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* exponentiation or a multiplication.
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*/
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#include "libm.h"
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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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double scalbn(double x, int n)
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{
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// FIXME: k+n check depends on signed int overflow.. use unsigned hx
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// TODO: when long != int:
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// scalbln(x,long n) { if(n>9999)n=9999; else if(n<-9999)n=-9999; return scalbn(x,n); }
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// TODO: n < -50000 ...
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int32_t k,hx,lx;
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double scale;
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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) /* +-0 */
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return x;
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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)
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return tiny*x; /*underflow*/
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if (n > 1023) {
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x *= 0x1p1023;
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n -= 1023;
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if (n > 1023) {
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x *= 0x1p1023;
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n -= 1023;
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if (n > 1023)
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return x * 0x1p1023;
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}
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} else if (n < -1022) {
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x *= 0x1p-1022;
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n += 1022;
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if (n < -1022) {
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x *= 0x1p-1022;
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n += 1022;
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if (n < -1022)
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return x * 0x1p-1022;
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}
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}
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if (k == 0x7ff) /* NaN or Inf */
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return x + x;
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k = k + n;
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if (k > 0x7fe)
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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));
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return x;
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}
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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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return tiny*copysign(tiny, x); /*underflow*/
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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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INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
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return x * scale;
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}
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@ -1,54 +1,28 @@
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/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbnf.c */
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/*
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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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 "libm.h"
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static const float
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two25 = 3.355443200e+07, /* 0x4c000000 */
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twom25 = 2.9802322388e-08, /* 0x33000000 */
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huge = 1.0e+30,
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tiny = 1.0e-30;
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float scalbnf(float x, int n)
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{
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int32_t k, ix;
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GET_FLOAT_WORD(ix, x);
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k = (ix&0x7f800000)>>23; /* extract exponent */
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if (k == 0) { /* 0 or subnormal x */
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if ((ix&0x7fffffff) == 0) /* +-0 */
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return x;
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x *= two25;
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GET_FLOAT_WORD(ix, x);
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k = ((ix&0x7f800000)>>23) - 25;
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if (n < -50000)
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return tiny*x; /*underflow*/
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float scale;
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if (n > 127) {
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x *= 0x1p127f;
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n -= 127;
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if (n > 127) {
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x *= 0x1p127f;
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n -= 127;
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if (n > 127)
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return x * 0x1p127f;
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}
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} else if (n < -126) {
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x *= 0x1p-126f;
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n += 126;
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if (n < -126) {
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x *= 0x1p-126f;
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n += 126;
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if (n < -126)
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return x * 0x1p-126f;
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}
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}
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if (k == 0xff) /* NaN or Inf */
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return x + x;
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k = k + n;
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if (k > 0xfe)
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return huge*copysignf(huge, x); /* overflow */
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if (k > 0) { /* normal result */
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SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23));
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return x;
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}
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if (k <= -25)
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if (n > 50000) /* in case integer overflow in n+k */
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return huge*copysignf(huge,x); /*overflow*/
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return tiny*copysignf(tiny, x); /*underflow*/
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k += 25; /* subnormal result */
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SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23));
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return x*twom25;
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SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23);
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return x * scale;
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}
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@ -1,21 +1,3 @@
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/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbnl.c */
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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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/*
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* scalbnl (long double x, int n)
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* scalbnl(x,n) returns x* 2**n computed by exponent
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* manipulation rather than by actually performing an
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* exponentiation or a multiplication.
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*/
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#include "libm.h"
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#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
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@ -24,40 +6,31 @@ long double scalbnl(long double x, int n)
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return scalbn(x, n);
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}
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#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
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static const long double
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huge = 0x1p16000L,
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tiny = 0x1p-16000L;
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long double scalbnl(long double x, int n)
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{
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union IEEEl2bits u;
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int k;
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union IEEEl2bits scale;
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u.e = x;
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k = u.bits.exp; /* extract exponent */
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if (k == 0) { /* 0 or subnormal x */
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if ((u.bits.manh|u.bits.manl) == 0) /* +-0 */
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return x;
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u.e *= 0x1p128;
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k = u.bits.exp - 128;
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if (n < -50000)
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return tiny*x; /*underflow*/
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if (n > 16383) {
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x *= 0x1p16383L;
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n -= 16383;
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if (n > 16383) {
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x *= 0x1p16383L;
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n -= 16383;
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if (n > 16383)
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return x * 0x1p16383L;
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}
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} else if (n < -16382) {
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x *= 0x1p-16382L;
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n += 16382;
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if (n < -16382) {
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x *= 0x1p-16382L;
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n += 16382;
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if (n < -16382)
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return x * 0x1p-16382L;
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}
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}
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if (k == 0x7fff) /* NaN or Inf */
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return x + x;
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k = k + n;
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if (k >= 0x7fff)
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return huge*copysignl(huge, x); /* overflow */
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if (k > 0) { /* normal result */
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u.bits.exp = k;
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return u.e;
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}
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if (k <= -128)
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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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return tiny*copysign(tiny, x); /*underflow*/
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k += 128; /* subnormal result */
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u.bits.exp = k;
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return u.e*0x1p-128;
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scale.e = 1.0L;
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scale.bits.exp = 0x3fff + n;
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return x * scale.e;
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}
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#endif
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