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simplify scalbn*.c implementations

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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)
This commit is contained in:
nsz
2012-03-19 10:54:07 +01:00
parent f767aba8af
commit 8051e08e10
3 changed files with 65 additions and 152 deletions
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70
src/math/scalbnf.c
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@ -1,54 +1,28 @@
/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbnf.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
*/
/*
* ====================================================
* 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 "libm.h"
static const float
two25 = 3.355443200e+07, /* 0x4c000000 */
twom25 = 2.9802322388e-08, /* 0x33000000 */
huge = 1.0e+30,
tiny = 1.0e-30;
float scalbnf(float x, int n)
{
int32_t k, ix;
GET_FLOAT_WORD(ix, x);
k = (ix&0x7f800000)>>23; /* extract exponent */
if (k == 0) { /* 0 or subnormal x */
if ((ix&0x7fffffff) == 0) /* +-0 */
return x;
x *= two25;
GET_FLOAT_WORD(ix, x);
k = ((ix&0x7f800000)>>23) - 25;
if (n < -50000)
return tiny*x; /*underflow*/
float scale;
if (n > 127) {
x *= 0x1p127f;
n -= 127;
if (n > 127) {
x *= 0x1p127f;
n -= 127;
if (n > 127)
return x * 0x1p127f;
}
} else if (n < -126) {
x *= 0x1p-126f;
n += 126;
if (n < -126) {
x *= 0x1p-126f;
n += 126;
if (n < -126)
return x * 0x1p-126f;
}
}
if (k == 0xff) /* NaN or Inf */
return x + x;
k = k + n;
if (k > 0xfe)
return huge*copysignf(huge, x); /* overflow */
if (k > 0) { /* normal result */
SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23));
return x;
}
if (k <= -25)
if (n > 50000) /* in case integer overflow in n+k */
return huge*copysignf(huge,x); /*overflow*/
return tiny*copysignf(tiny, x); /*underflow*/
k += 25; /* subnormal result */
SET_FLOAT_WORD(x, (ix&0x807fffff)|(k<<23));
return x*twom25;
SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23);
return x * scale;
}