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
     1 /* @(#)s_scalbn.c 5.1 93/09/24 */
     2 /*
     3  * ====================================================
     4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     5  *
     6  * Developed at SunPro, a Sun Microsystems, Inc. business.
     7  * Permission to use, copy, modify, and distribute this
     8  * software is freely granted, provided that this notice
     9  * is preserved.
    10  * ====================================================
    11  */
    12 
    13 #if defined(LIBM_SCCS) && !defined(lint)
    14 static const char rcsid[] =
    15     "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
    16 #endif
    17 
    18 /*
    19  * scalbn (double x, int n)
    20  * scalbn(x,n) returns x* 2**n  computed by  exponent
    21  * manipulation rather than by actually performing an
    22  * exponentiation or a multiplication.
    23  */
    24 
    25 #include "math.h"
    26 #include "math_private.h"
    27 
    28 libm_hidden_proto(copysign)
    29 #ifdef __STDC__
    30      static const double
    31 #else
    32      static double
    33 #endif
    34        two54 = 1.80143985094819840000e+16,      /* 0x43500000, 0x00000000 */
    35          twom54 = 5.55111512312578270212e-17,   /* 0x3C900000, 0x00000000 */
    36          huge = 1.0e+300, tiny = 1.0e-300;
    37 
    38 libm_hidden_proto(scalbn)
    39 #ifdef __STDC__
    40      double scalbn(double x, int n)
    41 #else
    42      double scalbn(x, n)
    43      double x;
    44      int n;
    45 #endif
    46 {
    47     int32_t k, hx, lx;
    48     EXTRACT_WORDS(hx, lx, x);
    49     k = (hx & 0x7ff00000) >> 20;        /* extract exponent */
    50     if (k == 0) {               /* 0 or subnormal x */
    51         if ((lx | (hx & 0x7fffffff)) == 0)
    52             return x;           /* +-0 */
    53         x *= two54;
    54         GET_HIGH_WORD(hx, x);
    55         k = ((hx & 0x7ff00000) >> 20) - 54;
    56         if (n < -50000)
    57             return tiny * x;    /*underflow */
    58     }
    59     if (k == 0x7ff)
    60         return x + x;           /* NaN or Inf */
    61     k = k + n;
    62     if (k > 0x7fe)
    63         return huge * copysign(huge, x);        /* overflow  */
    64     if (k > 0) {                /* normal result */
    65         SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    66         return x;
    67     }
    68     if (k <= -54) {
    69         if (n > 50000)          /* in case integer overflow in n+k */
    70             return huge * copysign(huge, x);    /*overflow */
    71         else
    72             return tiny * copysign(tiny, x);    /*underflow */
    73     }
    74     k += 54;                    /* subnormal result */
    75     SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    76     return x * twom54;
    77 }
    78 
    79 libm_hidden_def(scalbn)