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math: rewrite rounding functions (ceil, floor, trunc, round, rint)

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* faster, smaller, cleaner implementation than the bit hacks of fdlibm
* use arithmetics like y=(double)(x+0x1p52)-0x1p52, which is an integer
neighbor of x in all rounding modes (0<=x<0x1p52) and only use bithacks
when that's faster and smaller (for float it usually is)
* the code assumes standard excess precision handling for casts
* long double code supports both ld80 and ld128
* nearbyint is not changed (it is a wrapper around rint)
This commit is contained in:
Szabolcs Nagy
2013-09-03 03:27:02 +00:00
parent 98be442ee8
commit d1a2ead878
15 changed files with 273 additions and 904 deletions
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59
src/math/truncf.c
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@ -1,52 +1,19 @@
/* origin: FreeBSD /usr/src/lib/msun/src/s_truncf.c */
/*
* ====================================================
* 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.
* ====================================================
*/
/*
* truncf(x)
* Return x rounded toward 0 to integral value
* Method:
* Bit twiddling.
* Exception:
* Inexact flag raised if x not equal to truncf(x).
*/
#include "libm.h"
static const float huge = 1.0e30f;
float truncf(float x)
{
int32_t i0,j0;
uint32_t i;
union {float f; uint32_t i;} u = {x};
int e = (int)(u.i >> 23 & 0xff) - 0x7f + 9;
uint32_t m;
GET_FLOAT_WORD(i0, x);
j0 = ((i0>>23)&0xff) - 0x7f;
if (j0 < 23) {
if (j0 < 0) { /* |x|<1, return 0*sign(x) */
/* raise inexact if x != 0 */
if (huge+x > 0.0f)
i0 &= 0x80000000;
} else {
i = 0x007fffff>>j0;
if ((i0&i) == 0)
return x; /* x is integral */
/* raise inexact */
if (huge+x > 0.0f)
i0 &= ~i;
}
} else {
if (j0 == 0x80)
return x + x; /* inf or NaN */
return x; /* x is integral */
}
SET_FLOAT_WORD(x, i0);
return x;
if (e >= 23 + 9)
return x;
if (e < 9)
e = 1;
m = -1U >> e;
if ((u.i & m) == 0)
return x;
FORCE_EVAL(x + 0x1p120f);
u.i &= ~m;
return u.f;
}