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Diffstat (limited to 'sysdeps/powerpc/q_qtos.c')
| -rw-r--r-- | sysdeps/powerpc/q_qtos.c | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/sysdeps/powerpc/q_qtos.c b/sysdeps/powerpc/q_qtos.c new file mode 100644 index 0000000000..cd2715f8e9 --- /dev/null +++ b/sysdeps/powerpc/q_qtos.c @@ -0,0 +1,84 @@ +/* 128-bit floating point to 32-bit floating point. + Copyright (C) 1997 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Library General Public License as + published by the Free Software Foundation; either version 2 of the + License, or (at your option) any later version. + + The GNU C Library 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. */ + +#include <quad_float.h> + +/* float _q_qtos(const long double *a); + Convert 'a' to float. Round as per current rounding flags. + + Input Rounding Output + +/-0 * +/-0 + +/-Inf * +/-Inf + +/-NaN * +/-NaN (with mantissa truncated) + +/-SNaN * +/-NaN (with mantissa truncated, MSB of mantissa <- 1) + && raise VXSNAN + [Note: just truncating the mantissa may not give you + a SNaN!] + |a|>=2^128 Nearest +/-Inf && raise overflow && raise inexact + |a|>=2^128 Truncate +/-(2^128-2^104) && raise overflow && raise inexact + a>=2^128 +Inf +Inf && raise overflow && raise inexact + a<=-2^128 +Inf -(2^128-2^104) && raise overflow && raise inexact + a>=2^128 -Inf +(2^128-2^104) && raise overflow && raise inexact + a<=-2^128 -Inf -Inf && raise overflow && raise inexact + + We also need to raise 'inexact' if the result will be inexact, which + depends on the current rounding mode. + + To avoid having to deal with all that, we convert to a 'double' + that will round correctly (but is not itself rounded correctly), + and convert that to a float. This makes this procedure much + simpler and much faster. */ + +float +__q_qtos(const unsigned long long a[2]) +{ + unsigned long long a0,d; + union { + double d; + unsigned long long ull; + } u; + + a0 = a[0]; + + /* Truncate the mantissa to 48 bits. */ + d = a0 << 4; + /* Set the low bit in the mantissa if any of the bits we are dropping + were 1. This ensures correct rounding, and also distinguishes + 0 and Inf from denormalised numbers and SNaN (respectively). */ + d |= a[1] != 0; + /* Copy the sign bit. */ + d = d & 0x7fffffffffffffffULL | a0 & 0x8000000000000000ULL; + + /* Now, we need to fix the exponent. If the exponent of a was in + the range +127 to -152, or was +16384 or -16383, it is already + correct in 'd'. Otherwise, we need to ensure that the new + exponent is in the range +1023 to +128, or -153 to -1022, with + the same sign as the exponent of 'a'. We can do this by setting + bits 1-3 (the second through fourth-most significant bit) of 'd' + to 101 if bit 1 of 'a' is 1, or 010 if bit 1 of 'a' is 0. */ + if ((a0 >> 56 & 0x7f) - 0x3f > 1) + { + unsigned t = (a0 >> 32+2 & 2 << 31-1-2)*3 + (2 << 31-2); + d = (d & 0x8fffffffffffffffULL + | (unsigned long long)t<<32 & 0x7000000000000000ULL); + } + + u.ull = d; + return (float)u.d; +} |