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cogl: Add a fallback for when the signbit macro is missing

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The signbit macro is defined in C99 so it should be available but some
versions of GCC don't appear to define it by default. If it's not
available we can use a hack to test the bit directly.
This commit is contained in:
Neil Roberts 2010-02-11 14:20:48 +00:00
parent a0a40f07b3
commit f74f4bdc2b
3 changed files with 28 additions and 3 deletions
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2
cogl/cogl-sub-texture.c
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@ -124,7 +124,7 @@ _cogl_sub_texture_unmap_coord (gfloat t,
/* Convert the fractional part leaving the integer part in tact */
frac_part = modff (t, &int_part);
if (signbit (frac_part))
if (cogl_util_float_signbit (frac_part))
frac_part = ((1.0f + frac_part) * full_size -
sub_offset - sub_size) / sub_size;
else

2
cogl/cogl-texture-2d.c
View file

@ -64,7 +64,7 @@ _cogl_texture_2d_wrap_coords (float t_1, float t_2,
modff (t_1 < t_2 ? t_1 : t_2, &int_part);
t_1 -= int_part;
t_2 -= int_part;
if (signbit (int_part))
if (cogl_util_float_signbit (int_part))
{
*out_t_1 = 1.0f + t_1;
*out_t_2 = 1.0f + t_2;

27
cogl/cogl-util.h
View file

@ -3,7 +3,7 @@
*
* An object oriented GL/GLES Abstraction/Utility Layer
*
* Copyright (C) 2007,2008,2009 Intel Corporation.
* Copyright (C) 2007,2008,2009,2010 Intel Corporation.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@ -24,7 +24,32 @@
#ifndef __COGL_UTIL_H
#define __COGL_UTIL_H
#include <glib.h>
#include <math.h>
int
cogl_util_next_p2 (int a);
/* The signbit macro is defined by ISO C99 so it should be available,
however if it's not we can fallback to an evil hack */
#ifdef signbit
#define cogl_util_float_signbit(x) signbit(x)
#else
/* This trick was stolen from here:
http://lists.boost.org/Archives/boost/2006/08/108731.php
It xors the integer reinterpretations of -1.0f and 1.0f. In theory
they should only differ by the signbit so that gives a mask for the
sign which we can just test against the value */
static inline gboolean
cogl_util_float_signbit (float x)
{
static const union { float f; guint32 i; } negative_one = { -1.0f };
static const union { float f; guint32 i; } positive_one = { +1.0f };
union { float f; guint32 i; } value = { x };
return !!((negative_one.i ^ positive_one.i) & value.i);
}
#endif
#endif /* __COGL_UTIL_H */