src/libm/s_floor.c
author Sam Lantinga <slouken@libsdl.org>
Sat, 04 Oct 2008 06:46:59 +0000
changeset 2765 f55c87ae336b
parent 2760 02aa80d7905f
child 3162 dc1eb82ffdaa
permissions -rw-r--r--
Final merge of Google Summer of Code 2008 work...

Bring SDL to iPhone and iPod Touch
by Holmes Futrell, mentored by Sam Lantinga
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/* @(#)s_floor.c 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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#if defined(LIBM_SCCS) && !defined(lint)
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static char rcsid[] =
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    "$NetBSD: s_floor.c,v 1.8 1995/05/10 20:47:20 jtc Exp $";
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#endif
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/*
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 * floor(x)
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 * Return x rounded toward -inf to integral value
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 * Method:
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 *	Bit twiddling.
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 * Exception:
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 *	Inexact flag raised if x not equal to floor(x).
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 */
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#include "math.h"
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#include "math_private.h"
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#ifdef __STDC__
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static const double huge = 1.0e300;
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#else
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static double huge = 1.0e300;
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#endif
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libm_hidden_proto(floor)
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#ifdef __STDC__
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     double floor(double x)
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#else
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     double floor(x)
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     double x;
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#endif
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{
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    int32_t i0, i1, j0;
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    u_int32_t i, j;
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    EXTRACT_WORDS(i0, i1, x);
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    j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
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    if (j0 < 20) {
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        if (j0 < 0) {           /* raise inexact if x != 0 */
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            if (huge + x > 0.0) {       /* return 0*sign(x) if |x|<1 */
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                if (i0 >= 0) {
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                    i0 = i1 = 0;
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                } else if (((i0 & 0x7fffffff) | i1) != 0) {
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                    i0 = 0xbff00000;
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                    i1 = 0;
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                }
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            }
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        } else {
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            i = (0x000fffff) >> j0;
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            if (((i0 & i) | i1) == 0)
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                return x;       /* x is integral */
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            if (huge + x > 0.0) {       /* raise inexact flag */
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                if (i0 < 0)
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                    i0 += (0x00100000) >> j0;
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                i0 &= (~i);
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                i1 = 0;
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            }
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        }
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    } else if (j0 > 51) {
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        if (j0 == 0x400)
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            return x + x;       /* inf or NaN */
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        else
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            return x;           /* x is integral */
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    } else {
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        i = ((u_int32_t) (0xffffffff)) >> (j0 - 20);
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        if ((i1 & i) == 0)
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            return x;           /* x is integral */
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        if (huge + x > 0.0) {   /* raise inexact flag */
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            if (i0 < 0) {
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                if (j0 == 20)
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                    i0 += 1;
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                else {
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                    j = i1 + (1 << (52 - j0));
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                    if (j < (u_int32_t) i1)
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                        i0 += 1;        /* got a carry */
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                    i1 = j;
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                }
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            }
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            i1 &= (~i);
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        }
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    }
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    INSERT_WORDS(x, i0, i1);
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    return x;
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}
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libm_hidden_def(floor)