ftoastr: new module, for lossless conversion of floats to short strings

* lib/ftoastr.h, lib/ftoastr.c, lib/dtoastr.c, lib/ldtoastr.c:
* modules/ftoastr: New files.

1 files changed, 89 insertions, 0 deletions

diff --git a/lib/ftoastr.c b/lib/ftoastr.c
new file mode 100644
index 0000000000..25e0705e42
--- /dev/null
+++ b/lib/ftoastr.c
@@ -0,0 +1,89 @@
+/* floating point to accurate string
+
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   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 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, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include "ftoastr.h"
+
+#include "intprops.h"
+#include <float.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if LENGTH == 3
+# define FLOAT long double
+# define FLOAT_DIG LDBL_DIG
+# define FLOAT_MIN LDBL_MIN
+# define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
+# define FTOASTR ldtoastr
+# define STRTOF strtold
+#elif LENGTH == 2
+# define FLOAT double
+# define FLOAT_DIG DBL_DIG
+# define FLOAT_MIN DBL_MIN
+# define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
+# define FTOASTR dtoastr
+# define STRTOF strtod
+#else
+# define LENGTH 1
+# define FLOAT float
+# define FLOAT_DIG FLT_DIG
+# define FLOAT_MIN FLT_MIN
+# define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
+# define FTOASTR ftoastr
+# define STRTOF strtof
+#endif
+
+int
+FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
+{
+  /* The following method is simple but slow.
+     For ideas about speeding things up, please see:
+
+     Florian Loitsch, Printing floating-point numbers quickly and accurately
+     with integers.  ACM SIGPLAN notices 46, 6 (June 2010), 233-243
+     <http://dx.doi.org/10.1145/1809028.1806623>.  */
+
+  char format[sizeof "%-+ 0*.*Lg"];
+  FLOAT abs_x = x < 0 ? -x : x;
+  int prec;
+
+  char *p = format;
+  *p++ = '%';
+
+  /* Support flags that generate output parsable by strtof.  */
+  *p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY  ) != 0;
+  *p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
+  *p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
+  *p = '0'; p += (flags & FTOASTR_ZERO_PAD      ) != 0;
+
+  *p++ = '*';
+  *p++ = '.';
+  *p++ = '*';
+  *p = 'L'; p += 2 < LENGTH;
+  *p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
+  *p = '\0';
+
+  for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
+    {
+      int n = snprintf (buf, bufsize, format, width, prec, x);
+      if (n < 0
+          || FLOAT_PREC_BOUND <= prec
+          || (n < bufsize && STRTOF (buf, NULL) == x))
+        return n;
+    }
+}