X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;ds=sidebyside;f=lib%2Ftrunc.c;h=a10184e352a59c1a3e90825f97887f62c0a96061;hb=a3984e06bca84a7654624dd754a7c4c7a5a39a59;hp=b74021ee1f0dd3b9faeb99729c596cb42d842806;hpb=ec0af5d579654eb83aafc76940412b3bc106d558;p=gnulib.git
diff --git a/lib/trunc.c b/lib/trunc.c
index b74021ee1..a10184e35 100644
--- a/lib/trunc.c
+++ b/lib/trunc.c
@@ -1,19 +1,18 @@
/* Round towards zero.
Copyright (C) 2007 Free Software Foundation, Inc.
- This program is free software; you can redistribute it and/or modify
+ This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2, or (at your option)
- any later version.
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
- You should have received a copy of the GNU General Public License along
- with this program; if not, write to the Free Software Foundation,
- Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see . */
/* Written by Bruno Haible , 2007. */
@@ -24,18 +23,36 @@
#include
-/* 2^(DBL_MANT_DIG-1). */
-static const double TWO_MANT_DIG =
- /* Assume DBL_MANT_DIG <= 4 * 31.
+#ifdef USE_LONG_DOUBLE
+# define FUNC truncl
+# define DOUBLE long double
+# define MANT_DIG LDBL_MANT_DIG
+# define L_(literal) literal##L
+#elif ! defined USE_FLOAT
+# define FUNC trunc
+# define DOUBLE double
+# define MANT_DIG DBL_MANT_DIG
+# define L_(literal) literal
+#else /* defined USE_FLOAT */
+# define FUNC truncf
+# define DOUBLE float
+# define MANT_DIG FLT_MANT_DIG
+# define L_(literal) literal##f
+#endif
+
+/* 2^(MANT_DIG-1). */
+static const DOUBLE TWO_MANT_DIG =
+ /* Assume MANT_DIG <= 5 * 31.
Use the identity
- n = floor(n/4) + floor((n+1)/4) + floor((n+2)/4) + floor((n+3)/4). */
- (double) (1U << ((DBL_MANT_DIG - 1) / 4))
- * (double) (1U << ((DBL_MANT_DIG - 1 + 1) / 4))
- * (double) (1U << ((DBL_MANT_DIG - 1 + 2) / 4))
- * (double) (1U << ((DBL_MANT_DIG - 1 + 3) / 4));
+ n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */
+ (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
+ * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
+ * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
+ * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
+ * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
-double
-trunc (double x)
+DOUBLE
+FUNC (DOUBLE x)
{
/* The use of 'volatile' guarantees that excess precision bits are dropped
at each addition step and before the following comparison at the caller's
@@ -43,26 +60,34 @@ trunc (double x)
compliant by default, to avoid that the results become platform and compiler
option dependent. 'volatile' is a portable alternative to gcc's
-ffloat-store option. */
- volatile double y = x;
- volatile double z = y;
+ volatile DOUBLE y = x;
+ volatile DOUBLE z = y;
- if (z > 0)
+ if (z > L_(0.0))
{
- /* Round to the next integer (nearest or up or down, doesn't matter). */
- z += TWO_MANT_DIG;
- z -= TWO_MANT_DIG;
- /* Enforce rounding down. */
- if (z > y)
- z -= 1.0;
+ /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */
+ if (z < TWO_MANT_DIG)
+ {
+ /* Round to the next integer (nearest or up or down, doesn't matter). */
+ z += TWO_MANT_DIG;
+ z -= TWO_MANT_DIG;
+ /* Enforce rounding down. */
+ if (z > y)
+ z -= L_(1.0);
+ }
}
- else if (z < 0)
+ else if (z < L_(0.0))
{
- /* Round to the next integer (nearest or up or down, doesn't matter). */
- z -= TWO_MANT_DIG;
- z += TWO_MANT_DIG;
- /* Enforce rounding up. */
- if (z < y)
- z += 1.0;
+ /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */
+ if (z > - TWO_MANT_DIG)
+ {
+ /* Round to the next integer (nearest or up or down, doesn't matter). */
+ z -= TWO_MANT_DIG;
+ z += TWO_MANT_DIG;
+ /* Enforce rounding up. */
+ if (z < y)
+ z += L_(1.0);
+ }
}
return z;
}