src/libm/s_scalbn.c
author Sam Lantinga <slouken@libsdl.org>
Wed, 03 Jun 2009 04:37:27 +0000
changeset 3162 dc1eb82ffdaa
parent 2756 a98604b691c8
child 3337 9ac6f0782dd6
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_scalbn.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_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
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#endif
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/*
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 * scalbn (double x, int n)
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 * scalbn(x,n) returns x* 2**n  computed by  exponent
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 * manipulation rather than by actually performing an
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 * exponentiation or a multiplication.
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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(copysign)
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#ifdef __STDC__
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     static const double
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#else
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     static double
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#endif
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       two54 = 1.80143985094819840000e+16,      /* 0x43500000, 0x00000000 */
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         twom54 = 5.55111512312578270212e-17,   /* 0x3C900000, 0x00000000 */
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         huge = 1.0e+300, tiny = 1.0e-300;
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libm_hidden_proto(scalbn)
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#ifdef __STDC__
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     double scalbn(double x, int n)
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#else
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     double scalbn(x, n)
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     double x;
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     int n;
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#endif
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{
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    int32_t k, hx, lx;
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    EXTRACT_WORDS(hx, lx, x);
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    k = (hx & 0x7ff00000) >> 20;        /* extract exponent */
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    if (k == 0) {               /* 0 or subnormal x */
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        if ((lx | (hx & 0x7fffffff)) == 0)
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            return x;           /* +-0 */
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        x *= two54;
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        GET_HIGH_WORD(hx, x);
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        k = ((hx & 0x7ff00000) >> 20) - 54;
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        if (n < -50000)
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            return tiny * x;    /*underflow */
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    }
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    if (k == 0x7ff)
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        return x + x;           /* NaN or Inf */
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    k = k + n;
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    if (k > 0x7fe)
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        return huge * copysign(huge, x);        /* overflow  */
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    if (k > 0) {                /* normal result */
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        SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
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        return x;
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    }
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    if (k <= -54) {
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        if (n > 50000)          /* in case integer overflow in n+k */
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            return huge * copysign(huge, x);    /*overflow */
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        else
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            return tiny * copysign(tiny, x);    /*underflow */
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    }
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    k += 54;                    /* subnormal result */
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    SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
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    return x * twom54;
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}
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libm_hidden_def(scalbn)