Add strfromd, strfromf, and strfroml functions

ISO/IEC TS 18661-1 adds several functions in the strfrom family to stdlib.
This patch adds strfromd, strfromf, and strfroml.  This is being done in
preparation for the new floating-point type, float128.  The added functions
convert a floating-point value into a string, with configurable format.

1 files changed, 149 insertions, 0 deletions

diff --git a/stdlib/strfrom-skeleton.c b/stdlib/strfrom-skeleton.c
new file mode 100644
index 0000000000..8fd1beb7aa
--- /dev/null
+++ b/stdlib/strfrom-skeleton.c
@@ -0,0 +1,149 @@
+/* Convert a floating-point number to string.
+   Copyright (C) 2016 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 Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Generic implementation for strfrom functions.  The implementation is generic
+   for several floating-point types (e.g.: float, double), so that each
+   function, such as strfromf and strfroml, share the same code, thus avoiding
+   code duplication.  */
+
+#include <ctype.h>
+#include "../libio/libioP.h"
+#include "../libio/strfile.h"
+#include <printf.h>
+#include <string.h>
+#include <locale/localeinfo.h>
+
+#define UCHAR_T char
+#define L_(Str) Str
+#define ISDIGIT(Ch) isdigit (Ch)
+#include "stdio-common/printf-parse.h"
+
+int
+STRFROM (char *dest, size_t size, const char *format, FLOAT f)
+{
+  _IO_strnfile sfile;
+#ifdef _IO_MTSAFE_IO
+  sfile.f._sbf._f._lock = NULL;
+#endif
+
+  int done;
+
+  /* Single-precision values need to be stored in a double type, because
+     __printf_fp_l and __printf_fphex do not accept the float type.  */
+  union {
+    double flt;
+    FLOAT value;
+  } fpnum;
+  const void *fpptr;
+  fpptr = &fpnum;
+
+  /* Variables to control the output format.  */
+  int precision = -1; /* printf_fp and printf_fphex treat this internally.  */
+  int specifier;
+  struct printf_info info;
+
+  /* Single-precision values need to be converted into double-precision,
+     because __printf_fp and __printf_fphex only accept double and long double
+     as the floating-point argument.  */
+  if (__builtin_types_compatible_p (FLOAT, float))
+    fpnum.flt = f;
+  else
+    fpnum.value = f;
+
+  /* Check if the first character in the format string is indeed the '%'
+     character.  Otherwise, abort.  */
+  if (*format == '%')
+    format++;
+  else
+    abort ();
+
+  /* The optional precision specification always starts with a '.'.  If such
+     character is present, read the precision.  */
+  if (*format == '.')
+    {
+      format++;
+
+      /* Parse the precision.  */
+      if (ISDIGIT (*format))
+	precision = read_int (&format);
+      /* If only the period is specified, the precision is taken as zero, as
+	 described in ISO/IEC 9899:2011, section 7.21.6.1, 4th paragraph, 3rd
+	 item.  */
+      else
+	precision = 0;
+    }
+
+  /* Now there is only the conversion specifier to be read.  */
+  switch (*format)
+    {
+    case 'a':
+    case 'A':
+    case 'e':
+    case 'E':
+    case 'f':
+    case 'F':
+    case 'g':
+    case 'G':
+      specifier = *format;
+      break;
+    default:
+      abort ();
+    }
+
+  /* The following code to prepare the virtual file has been adapted from the
+     function _IO_vsnprintf from libio.  */
+
+  if (size == 0)
+    {
+    /* When size is zero, nothing is written and dest may be a null pointer.
+       This is specified for snprintf in ISO/IEC 9899:2011, Section 7.21.6.5,
+       in the second paragraph.  Thus, if size is zero, prepare to use the
+       overflow buffer right from the start.  */
+      dest = sfile.overflow_buf;
+      size = sizeof (sfile.overflow_buf);
+    }
+
+  /* Prepare the virtual string file.  */
+  _IO_no_init (&sfile.f._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
+  _IO_JUMPS (&sfile.f._sbf) = &_IO_strn_jumps;
+  _IO_str_init_static_internal (&sfile.f, dest, size - 1, dest);
+
+  /* Prepare the format specification for printf_fp.  */
+  memset (&info, '\0', sizeof (info));
+
+  /* The functions strfromd and strfromf pass a floating-point number with
+     double precision to printf_fp, whereas strfroml passes a floating-point
+     number with long double precision.  The following line informs printf_fp
+     which type of floating-point number is being passed.  */
+  info.is_long_double = __builtin_types_compatible_p (FLOAT, long double);
+
+  /* Set info according to the format string.  */
+  info.prec = precision;
+  info.spec = specifier;
+
+  if (info.spec != 'a' && info.spec != 'A')
+    done = __printf_fp_l (&sfile.f._sbf._f, _NL_CURRENT_LOCALE, &info, &fpptr);
+  else
+    done = __printf_fphex (&sfile.f._sbf._f, &info, &fpptr);
+
+  /* Terminate the string.  */
+  if (sfile.f._sbf._f._IO_buf_base != sfile.overflow_buf)
+    *sfile.f._sbf._f._IO_write_ptr = '\0';
+
+  return done;
+}