1 files changed, 140 insertions, 0 deletions
diff --git a/lib/ftoastr.c b/lib/ftoastr.c
new file mode 100644
index 0000000..7a7d411
--- /dev/null
+++ b/lib/ftoastr.c
@@ -0,0 +1,140 @@
+/* floating point to accurate string
+
+   Copyright (C) 2010-2020 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 <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+/* This code can misbehave on some buggy or older platforms, when
+   operating on arguments on floating types other than 'double', or
+   when given unusual combinations of options.  Gnulib's
+   snprintf-posix module works around many of these problems.
+
+   This code relies on sprintf, strtod, etc. operating accurately;
+   otherwise, the resulting strings could be inaccurate or too long.  */
+
+#include <config.h>
+
+#include "ftoastr.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 PROMOTED_FLOAT long double
+# 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 PROMOTED_FLOAT double
+#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 PROMOTED_FLOAT double
+# if HAVE_STRTOF
+#  define STRTOF strtof
+# endif
+#endif
+
+/* On pre-C99 hosts, approximate strtof with strtod.  This
+   may generate one or two extra digits, but that's better than not
+   working at all.  */
+#ifndef STRTOF
+# define STRTOF strtod
+#endif
+
+/* On hosts where it's not known that snprintf works, use sprintf to
+   implement the subset needed here.  Typically BUFSIZE is big enough
+   and there's little or no performance hit.  */
+#if ! GNULIB_SNPRINTF
+# undef snprintf
+# define snprintf ftoastr_snprintf
+static int
+ftoastr_snprintf (char *buf, size_t bufsize, char const *format,
+                  int width, int prec, FLOAT x)
+{
+  PROMOTED_FLOAT promoted_x = x;
+  char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND
+                      : LENGTH == 2 ? DBL_BUFSIZE_BOUND
+                      : LDBL_BUFSIZE_BOUND];
+  int n = width;
+  if (bufsize < sizeof width_0_buffer)
+    {
+      n = sprintf (width_0_buffer, format, 0, prec, promoted_x);
+      if (n < 0)
+        return n;
+      if (n < width)
+        n = width;
+    }
+  if (n < bufsize)
+    n = sprintf (buf, format, width, prec, promoted_x);
+  return n;
+}
+#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:
+
+     Andrysco M, Jhala R, Lerner S. Printing floating-point numbers:
+     a faster, always correct method. ACM SIGPLAN notices - POPL '16.
+     2016;51(1):555-67 <https://doi.org/10.1145/2914770.2837654>; draft at
+     <https://cseweb.ucsd.edu/~lerner/papers/fp-printing-popl16.pdf>.  */
+
+  PROMOTED_FLOAT promoted_x = x;
+  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, promoted_x);
+      if (n < 0
+          || FLOAT_PREC_BOUND <= prec
+          || (n < bufsize && STRTOF (buf, NULL) == x))
+        return n;
+    }
+}