src/libm/s_copysign.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
slouken@2756
     1
/* @(#)s_copysign.c 5.1 93/09/24 */
slouken@2756
     2
/*
slouken@2756
     3
 * ====================================================
slouken@2756
     4
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
slouken@2756
     5
 *
slouken@2756
     6
 * Developed at SunPro, a Sun Microsystems, Inc. business.
slouken@2756
     7
 * Permission to use, copy, modify, and distribute this
slouken@2756
     8
 * software is freely granted, provided that this notice
slouken@2756
     9
 * is preserved.
slouken@2756
    10
 * ====================================================
slouken@2756
    11
 */
slouken@2756
    12
slouken@2756
    13
#if defined(LIBM_SCCS) && !defined(lint)
slouken@3162
    14
static const char rcsid[] =
slouken@2756
    15
    "$NetBSD: s_copysign.c,v 1.8 1995/05/10 20:46:57 jtc Exp $";
slouken@2756
    16
#endif
slouken@2756
    17
slouken@2756
    18
/*
slouken@2756
    19
 * copysign(double x, double y)
slouken@2756
    20
 * copysign(x,y) returns a value with the magnitude of x and
slouken@2756
    21
 * with the sign bit of y.
slouken@2756
    22
 */
slouken@2756
    23
slouken@2756
    24
#include "math.h"
slouken@2756
    25
#include "math_private.h"
slouken@2756
    26
slouken@2756
    27
libm_hidden_proto(copysign)
slouken@2756
    28
#ifdef __STDC__
slouken@2756
    29
     double copysign(double x, double y)
slouken@2756
    30
#else
slouken@2756
    31
     double copysign(x, y)
slouken@2756
    32
     double x, y;
slouken@2756
    33
#endif
slouken@2756
    34
{
slouken@2756
    35
    u_int32_t hx, hy;
slouken@2756
    36
    GET_HIGH_WORD(hx, x);
slouken@2756
    37
    GET_HIGH_WORD(hy, y);
slouken@2756
    38
    SET_HIGH_WORD(x, (hx & 0x7fffffff) | (hy & 0x80000000));
slouken@2756
    39
    return x;
slouken@2756
    40
}
slouken@2756
    41
slouken@2756
    42
libm_hidden_def(copysign)