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glibc  2.9
s_trunc.c
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00001 /* Copyright (C) 2007 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003    Contributed by Richard Henderson.
00004 
00005    The GNU C Library is free software; you can redistribute it and/or
00006    modify it under the terms of the GNU Lesser General Public
00007    License as published by the Free Software Foundation; either
00008    version 2.1 of the License, or (at your option) any later version.
00009 
00010    The GNU C Library is distributed in the hope that it will be useful,
00011    but WITHOUT ANY WARRANTY; without even the implied warranty of
00012    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00013    Lesser General Public License for more details.
00014 
00015    You should have received a copy of the GNU Lesser General Public
00016    License along with the GNU C Library; if not, write to the Free
00017    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00018    02111-1307 USA.  */
00019 
00020 #include <math.h>
00021 #include <math_ldbl_opt.h>
00022 
00023 
00024 /* Use the chopped rounding mode conversion instructions to implement trunc. */
00025 
00026 double
00027 __trunc (double x)
00028 {
00029   double two52 = copysign (0x1.0p52, x);
00030   double r, tmp;
00031   
00032   __asm (
00033 #ifdef _IEEE_FP_INEXACT
00034         "addt/suic %2, %3, %1\n\tsubt/suic %1, %3, %0"
00035 #else
00036         "addt/suc %2, %3, %1\n\tsubt/suc %1, %3, %0"
00037 #endif
00038         : "=&f"(r), "=&f"(tmp)
00039         : "f"(x), "f"(two52));
00040 
00041   /* trunc(-0) == -0, and in general we'll always have the same
00042      sign as our input.  */
00043   return copysign (r, x);
00044 }
00045 
00046 weak_alias (__trunc, trunc)
00047 #ifdef NO_LONG_DOUBLE
00048 strong_alias (__trunc, __truncl)
00049 weak_alias (__trunc, truncl)
00050 #endif
00051 #if LONG_DOUBLE_COMPAT(libm, GLIBC_2_1)
00052 compat_symbol (libm, __trunc, truncl, GLIBC_2_1);
00053 #endif