libio: Convert __vasprintf_internal to buffers

The buffer resizing algorithm is slightly different.  The initial
buffer is on the stack, and small buffers are directly allocated
on the heap using the exact required size.  The overhead of the
additional copy is compensated by the lowered setup cost for buffers
compared to libio streams.

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

libio/vasprintf.c

@@ -24,64 +24,115 @@
    This exception applies to code released by its copyright holders
    in files containing the exception.  */
 
-#include <string.h>
+#include <array_length.h>
+#include <errno.h>
+#include <limits.h>
+#include <math_ldbl_opt.h>
+#include <printf.h>
+#include <stdio.h>
 #include <stdlib.h>
-#include <strfile.h>
+#include <string.h>
+#include <printf_buffer.h>
+
+struct __printf_buffer_asprintf
+{
+  /* base.write_base points either to a heap-allocated buffer, or to
+     the direct array below.  */
+  struct __printf_buffer base;
+
+  /* Initial allocation.  200 should be large enough to copy almost
+     all asprintf usages with just a single (final, correctly sized)
+     heap allocation.  */
+  char direct[PRINTF_BUFFER_SIZE_ASPRINTF];
+};
+
+void
+__printf_buffer_flush_asprintf (struct __printf_buffer_asprintf *buf)
+{
+  size_t current_pos = buf->base.write_ptr - buf->base.write_base;
+  if (current_pos >= INT_MAX)
+    {
+      /* The result is not representable.  No need to continue.  */
+      __set_errno (EOVERFLOW);
+      __printf_buffer_mark_failed (&buf->base);
+      return;
+    }
+
+  size_t current_size = buf->base.write_end - buf->base.write_base;
+  /* Implement an exponentiation sizing policy.  Keep the size
+     congruent 8 (mod 16), to account for the footer in glibc
+     malloc.  */
+  size_t new_size = ALIGN_UP (current_size + current_size / 2, 16) | 8;
+  char *new_buffer;
+  if (buf->base.write_base == buf->direct)
+    {
+      new_buffer = malloc (new_size);
+      if (new_buffer == NULL)
+	{
+	  __printf_buffer_mark_failed (&buf->base);
+	  return;
+	}
+      memcpy (new_buffer, buf->direct, current_pos);
+    }
+  else
+    {
+      new_buffer = realloc (buf->base.write_base, new_size);
+      if (new_buffer == NULL)
+	{
+	  __printf_buffer_mark_failed (&buf->base);
+	  return;
+	}
+    }
+
+  /* Set up the new write area.  */
+  buf->base.write_base = new_buffer;
+  buf->base.write_ptr = new_buffer + current_pos;
+  buf->base.write_end = new_buffer + new_size;
+}
+
 
 int
 __vasprintf_internal (char **result_ptr, const char *format, va_list args,
 		      unsigned int mode_flags)
 {
-  /* Initial size of the buffer to be used.  Will be doubled each time an
-     overflow occurs.  */
-  const size_t init_string_size = 100;
-  char *string;
-  _IO_strfile sf;
-  int ret;
-  size_t needed;
-  size_t allocated;
-  /* No need to clear the memory here (unlike for open_memstream) since
-     we know we will never seek on the stream.  */
-  string = (char *) malloc (init_string_size);
-  if (string == NULL)
-    return -1;
-#ifdef _IO_MTSAFE_IO
-  sf._sbf._f._lock = NULL;
-#endif
-  _IO_no_init (&sf._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
-  _IO_JUMPS (&sf._sbf) = &_IO_str_jumps;
-  _IO_str_init_static_internal (&sf, string, init_string_size, string);
-  sf._sbf._f._flags &= ~_IO_USER_BUF;
-  sf._s._allocate_buffer_unused = (_IO_alloc_type) malloc;
-  sf._s._free_buffer_unused = (_IO_free_type) free;
-  ret = __vfprintf_internal (&sf._sbf._f, format, args, mode_flags);
-  if (ret < 0)
+  struct __printf_buffer_asprintf buf;
+  __printf_buffer_init (&buf.base, buf.direct, array_length (buf.direct),
+			__printf_buffer_mode_asprintf);
+
+  __printf_buffer (&buf.base, format, args, mode_flags);
+  int done = __printf_buffer_done (&buf.base);
+  if (done < 0)
     {
-      free (sf._sbf._f._IO_buf_base);
-      return ret;
+      if (buf.base.write_base != buf.direct)
+	free (buf.base.write_base);
+      return done;
+    }
+
+  /* Transfer to the final buffer.  */
+  char *result;
+  size_t size = buf.base.write_ptr - buf.base.write_base;
+  if (buf.base.write_base == buf.direct)
+    {
+      result = malloc (size + 1);
+      if (result == NULL)
+	return -1;
+      memcpy (result, buf.direct, size);
     }
-  /* Only use realloc if the size we need is of the same (binary)
-     order of magnitude then the memory we allocated.  */
-  needed = sf._sbf._f._IO_write_ptr - sf._sbf._f._IO_write_base + 1;
-  allocated = sf._sbf._f._IO_write_end - sf._sbf._f._IO_write_base;
-  if ((allocated >> 1) <= needed)
-    *result_ptr = (char *) realloc (sf._sbf._f._IO_buf_base, needed);
   else
     {
-      *result_ptr = (char *) malloc (needed);
-      if (*result_ptr != NULL)
+      result = realloc (buf.base.write_base, size + 1);
+      if (result == NULL)
 	{
-	  memcpy (*result_ptr, sf._sbf._f._IO_buf_base, needed - 1);
-	  free (sf._sbf._f._IO_buf_base);
+	  free (buf.base.write_base);
+	  return -1;
 	}
-      else
-	/* We have no choice, use the buffer we already have.  */
-	*result_ptr = (char *) realloc (sf._sbf._f._IO_buf_base, needed);
     }
-  if (*result_ptr == NULL)
-    *result_ptr = sf._sbf._f._IO_buf_base;
-  (*result_ptr)[needed - 1] = '\0';
-  return ret;
+
+  /* Add NUL termination.  */
+  result[size] = '\0';
+  *result_ptr = result;
+
+  return done;
 }
 
 int