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94 lines
2.6 KiB
C
94 lines
2.6 KiB
C
// Original source file copyright gcc.gnu.org, GNU Free Documentation License, Version 1.3.
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// Notes for Boost.Math, (contains Quickbook snippets as C/C++ comments - do not remove!)
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// Copyright Paul Bristow 2016.
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// Distributed under the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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//[quadmath_snprintf_1
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/*`Example of using GCC Quad-Precision Math Library quadmath `__float128` type,
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taking a square root with sqrtq, and output using quadmath_snprintf.
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From GCC Quad-Precision Math Library,
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[@https://gcc.gnu.org/onlinedocs/libquadmath.pdf 3.2 quadmath_snprintf, Convert to string]
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(pages 9 and 10).
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Requires GCC linker option `-lquadmath`.
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If this linker option is missing then you will get errors like:
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``
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/Cpp/float128/quadmath_snprintf/quadmath_snprintf.c:44: undefined reference to 'sqrtq'.
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/Cpp/float128/quadmath_snprintf/quadmath_snprintf.c:45: undefined reference to 'quadmath_snprintf'.
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``
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On one system, the header file (that contains all the `extern` declarations), included, for example:
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``
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extern __float128 sqrtq (__float128) __quadmath_throw;
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extern __float128 strtoflt128 (const char *, char **) __quadmath_throw;
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extern int quadmath_snprintf (char *str, size_t size, const char *format, ...) __quadmath_throw;
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``
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An example of a location of `quadmath.h` is
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``
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C:\program files\gcc-6-win64\lib\gcc\x86_64-w64-mingw32\6.1.1\include\quadmath.h
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``
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and library at
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``
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C:\Program Files\gcc-6-win64\bin\libquadmath-0.dll
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``
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Command lines used (using [@http://www.codeblocks.org CodeBLocks]:
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``
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gcc.exe -Wall -g -c J:\Cpp\float128\quadmath_snprintf\main.c -o obj\Debug\main.o
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g++.exe -o bin\Debug\quadmath_snprintf.exe obj\Debug\main.o -lquadmath
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``
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*/
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//] [/quadmath_snprintf_1]
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#include <quadmath.h>
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#include <stdlib.h>
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#include <stdio.h>
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int main ()
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{
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__float128 r;
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int prec = 20;
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int width = 46;
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char buf[128];
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r = 2.0q;
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r = sqrtq (r);
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int n = quadmath_snprintf (buf, sizeof buf, "%+-#*.20Qe", width, r);
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if ((size_t) n < sizeof buf)
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printf ("%s\n", buf);
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/* Prints: +1.41421356237309504880e+00 */
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quadmath_snprintf (buf, sizeof buf, "%Qa", r);
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if ((size_t) n < sizeof buf)
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printf ("%s\n", buf);
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/* Prints: 0x1.6a09e667f3bcc908b2fb1366ea96p+0 */
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n = quadmath_snprintf (NULL, 0, "%+-#46.*Qe", prec, r);
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if (n > -1)
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{
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char *str = malloc (n + 1);
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if (str)
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{
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quadmath_snprintf (str, n + 1, "%+-#46.*Qe", prec, r);
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printf ("%s\n", str);
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/* Prints: +1.41421356237309504880e+00 */
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}
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free (str);
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}
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return 0;
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}
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/*
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Output:
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+1.41421356237309504880e+00
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0x1.6a09e667f3bcc908b2fb1366ea96p+0
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+1.41421356237309504880e+00
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*/
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