src/libm/s_sin.c
author Sam Lantinga <slouken@libsdl.org>
Wed, 03 Jun 2009 04:37:27 +0000
changeset 3162 dc1eb82ffdaa
parent 2756 a98604b691c8
child 6044 35448a5ea044
permissions -rw-r--r--
Von: Thomas Zimmermann
Betreff: [SDL] [PATCH] Make static variables const
Datum: Tue, 19 May 2009 19:45:37 +0200

Hi,

this is a set of simple changes which make some of SDL's internal static
arrays constant. The purpose is to shrink the number of write-able
static bytes and thus increase the number of memory pages shared between
SDL applications.

The patch set is against trunk@4513. Each of the attached patch files is
specific to a sub-system. The set is completed by a second mail, because
of the list's 40 KiB limit.

The files readelf-r4513.txt and readelf-const-patch.txt where made by
calling 'readelf -S libSDL.so'. They show the difference in ELF sections
without and with the patch. Some numbers measured on my x86-64:

Before

[13] .rodata PROGBITS 00000000000eaaa0 000eaaa0
0000000000008170 0000000000000000 A 0 0 32
[19] .data.rel.ro PROGBITS 00000000003045e0 001045e0
00000000000023d0 0000000000000000 WA 0 0 32
[23] .data PROGBITS 00000000003076e0 001076e0
0000000000004988 0000000000000000 WA 0 0 32

After

[13] .rodata PROGBITS 00000000000eaaa0 000eaaa0
0000000000009a50 0000000000000000 A 0 0 32
[19] .data.rel.ro PROGBITS 0000000000306040 00106040
0000000000002608 0000000000000000 WA 0 0 32
[23] .data PROGBITS 0000000000309360 00109360
0000000000002e88 0000000000000000 WA 0 0 32

The size of the write-able data section decreased considerably. Some
entries became const-after-relocation, while most of its content went
straight into the read-only data section.

Best regards, Thomas
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/* @(#)s_sin.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 const char rcsid[] =
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    "$NetBSD: s_sin.c,v 1.7 1995/05/10 20:48:15 jtc Exp $";
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#endif
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/* sin(x)
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 * Return sine function of x.
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 *
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 * kernel function:
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 *	__kernel_sin		... sine function on [-pi/4,pi/4]
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 *	__kernel_cos		... cose function on [-pi/4,pi/4]
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 *	__ieee754_rem_pio2	... argument reduction routine
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 *
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 * Method.
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 *      Let S,C and T denote the sin, cos and tan respectively on
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 *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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 *	in [-pi/4 , +pi/4], and let n = k mod 4.
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 *	We have
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 *
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 *          n        sin(x)      cos(x)        tan(x)
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 *     ----------------------------------------------------------
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 *	    0	       S	   C		 T
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 *	    1	       C	  -S		-1/T
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 *	    2	      -S	  -C		 T
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 *	    3	      -C	   S		-1/T
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 *     ----------------------------------------------------------
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 *
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 * Special cases:
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 *      Let trig be any of sin, cos, or tan.
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 *      trig(+-INF)  is NaN, with signals;
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 *      trig(NaN)    is that NaN;
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 *
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 * Accuracy:
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 *	TRIG(x) returns trig(x) nearly rounded
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 */
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#include "math.h"
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#include "math_private.h"
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libm_hidden_proto(sin)
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#ifdef __STDC__
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     double sin(double x)
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#else
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     double sin(x)
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     double x;
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#endif
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{
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    double y[2], z = 0.0;
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    int32_t n, ix;
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    /* High word of x. */
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    GET_HIGH_WORD(ix, x);
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    /* |x| ~< pi/4 */
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    ix &= 0x7fffffff;
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    if (ix <= 0x3fe921fb)
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        return __kernel_sin(x, z, 0);
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    /* sin(Inf or NaN) is NaN */
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    else if (ix >= 0x7ff00000)
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        return x - x;
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    /* argument reduction needed */
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    else {
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        n = __ieee754_rem_pio2(x, y);
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        switch (n & 3) {
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        case 0:
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            return __kernel_sin(y[0], y[1], 1);
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        case 1:
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            return __kernel_cos(y[0], y[1]);
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        case 2:
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            return -__kernel_sin(y[0], y[1], 1);
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        default:
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            return -__kernel_cos(y[0], y[1]);
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        }
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    }
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}
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libm_hidden_def(sin)