stdio-common: Convert vfprintf and related functions to buffers

vfprintf is entangled with vfwprintf (of course), __printf_fp,
__printf_fphex, __vstrfmon_l_internal, and the strfrom family of
functions.  The latter use the internal snprintf functionality,
so vsnprintf is converted as well.

The simples conversion is __printf_fphex, followed by
__vstrfmon_l_internal and __printf_fp, and finally
__vfprintf_internal and __vfwprintf_internal.  __vsnprintf_internal
and strfrom* are mostly consuming the new interfaces, so they
are comparatively simple.

__printf_fp is a public symbol, so the FILE *-based interface
had to preserved.

The __printf_fp rewrite does not change the actual binary-to-decimal
conversion algorithm, and digits are still not emitted directly to
the target buffer.  However, the staging buffer now uses bytes
instead of wide characters, and one buffer copy is eliminated.

The changes are at least performance-neutral in my testing.
Floating point printing and snprintf improved measurably, so that
this Lua script

  for i=1,5000000 do
      print(i, i * math.pi)
  end

runs about 5% faster for me.  To preserve fprintf performance for
a simple "%d" format, this commit has some logic changes under
LABEL (unsigned_number) to avoid additional function calls.  There
are certainly some very easy performance improvements here: binary,
octal and hexadecimal formatting can easily avoid the temporary work
buffer (the number of digits can be computed ahead-of-time using one
of the __builtin_clz* built-ins). Decimal formatting can use a
specialized version of _itoa_word for base 10.

The existing (inconsistent) width handling between strfmon and printf
is preserved here.  __print_fp_buffer_1 would have to use
__translated_number_width to achieve ISO conformance for printf.

Test expectations in libio/tst-vtables-common.c are adjusted because
the internal staging buffer merges all virtual function calls into
one.

In general, stack buffer usage is greatly reduced, particularly for
unbuffered input streams.  __printf_fp can still use a large buffer
in binary128 mode for %g, though.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 21 insertions, 8 deletions

diff --git a/include/printf.h b/include/printf.h
index 5127a45f9b..2c998059d4 100644
--- a/include/printf.h
+++ b/include/printf.h
@@ -65,18 +65,31 @@ int __translated_number_width (locale_t loc,
 			       const char *first, const char *last)
   attribute_hidden;
 
-extern int __printf_fphex (FILE *, const struct printf_info *,
-			   const void *const *) attribute_hidden;
+
+struct __printf_buffer;
+void __printf_buffer (struct __printf_buffer *buf, const char *format,
+		      va_list ap, unsigned int mode_flags);
+struct __wprintf_buffer;
+void __wprintf_buffer (struct __wprintf_buffer *buf, const wchar_t *format,
+		       va_list ap, unsigned int mode_flags);
+
 extern int __printf_fp (FILE *, const struct printf_info *,
 			const void *const *);
 libc_hidden_proto (__printf_fp)
-extern int __printf_fp_l (FILE *, locale_t, const struct printf_info *,
-			  const void *const *);
-libc_hidden_proto (__printf_fp_l)
 
-extern unsigned int __guess_grouping (unsigned int intdig_max,
-				      const char *grouping)
-     attribute_hidden;
+void __printf_fphex_l_buffer (struct __printf_buffer *, locale_t,
+			      const struct printf_info *,
+			      const void *const *) attribute_hidden;
+void __printf_fp_l_buffer (struct __printf_buffer *, locale_t,
+			   const struct printf_info *,
+			   const void *const *) attribute_hidden;
+struct __wprintf_buffer;
+void __wprintf_fphex_l_buffer (struct __wprintf_buffer *, locale_t,
+			       const struct printf_info *,
+			       const void *const *) attribute_hidden;
+void __wprintf_fp_l_buffer (struct __wprintf_buffer *, locale_t,
+			    const struct printf_info *,
+			    const void *const *) attribute_hidden;
 
 # endif /* !_ISOMAC */
 #endif