Tune ‘format’ after recent fix

* doc/lispref/strings.texi (Formatting Strings):
* src/editfns.c (Fformat): Format field numbers no longer need
to be unique, reverting the previous doc change since that has
now been fixed.  Also, document that %% should not have modifiers.
* src/editfns.c (styled_format): Improve performance.  Remove
the need for the new prepass over the format string, by using
a typically-more-generous bound for the info array size.
Initialize the info array lazily.  Move string inspection to
the same area to help caching.  Avoid the need for a
converted_to_string bitfield by using EQ.  Cache arg in a
local and avoid some potential aliasing issues to help the
compiler.  Info array is now 0-origin, not 1-origin.

2 files changed, 72 insertions, 95 deletions

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index f365c80493d..23961f99efd 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -926,7 +926,8 @@ digit.
 
 @item %%
 Replace the specification with a single @samp{%}.  This format
-specification is unusual in that it does not use a value.  For example,
+specification is unusual in that its only form is plain
+@samp{%%} and that it does not use a value.  For example,
 @code{(format "%% %d" 30)} returns @code{"% 30"}.
 @end table
 
@@ -965,10 +966,9 @@ extra values to be formatted are ignored.
 decimal number immediately after the initial @samp{%}, followed by a
 literal dollar sign @samp{$}.  It causes the format specification to
 convert the argument with the given number instead of the next
-argument.  Field numbers start at 1.  A field number should differ
-from the other field numbers in the same format.  A format can contain
-either numbered or unnumbered format specifications but not both,
-except that @samp{%%} can be mixed with numbered specifications.
+argument.  Field numbers start at 1.  A format can contain either
+numbered or unnumbered format specifications but not both, except that
+@samp{%%} can be mixed with numbered specifications.
 
 @example
 (format "%2$s, %3$s, %%, %1$s" "x" "y" "z")
@@ -1026,8 +1026,7 @@ ignored.
   A specification can have a @dfn{width}, which is a decimal number
 that appears after any field number and flags.  If the printed
 representation of the object contains fewer characters than this
-width, @code{format} extends it with padding.  The width is
-ignored for the @samp{%%} specification.  Any padding introduced by
+width, @code{format} extends it with padding.  Any padding introduced by
 the width normally consists of spaces inserted on the left:
 
 @example
diff --git a/src/editfns.c b/src/editfns.c
index 56aa8ce1a72..43b17f9f116 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3891,8 +3891,8 @@ the next available argument, or the argument explicitly specified:
 The argument used for %d, %o, %x, %e, %f, %g or %c must be a number.
 Use %% to put a single % into the output.
 
-A %-sequence may contain optional field number, flag, width, and
-precision specifiers, as follows:
+A %-sequence other than %% may contain optional field number, flag,
+width, and precision specifiers, as follows:
 
   %<field><flags><width><precision>character
 
@@ -3901,10 +3901,9 @@ where field is [0-9]+ followed by a literal dollar "$", flags is
 followed by [0-9]+.
 
 If a %-sequence is numbered with a field with positive value N, the
-Nth argument is substituted instead of the next one.  A field number
-should differ from the other field numbers in the same format.  A
-format can contain either numbered or unnumbered %-sequences but not
-both, except that %% can be mixed with numbered %-sequences.
+Nth argument is substituted instead of the next one.  A format can
+contain either numbered or unnumbered %-sequences but not both, except
+that %% can be mixed with numbered %-sequences.
 
 The + flag character inserts a + before any positive number, while a
 space inserts a space before any positive number; these flags only
@@ -3980,49 +3979,40 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
   bool arg_intervals = false;
   USE_SAFE_ALLOCA;
 
-  /* Each element records, for one field,
-     the corresponding argument,
-     the start and end bytepos in the output string,
-     whether the argument has been converted to string (e.g., due to "%S"),
-     and whether the argument is a string with intervals.  */
+  /* Information recorded for each format spec.  */
   struct info
   {
+    /* The corresponding argument, converted to string if conversion
+       was needed.  */
     Lisp_Object argument;
+
+    /* The start and end bytepos in the output string.  */
     ptrdiff_t start, end;
-    bool_bf converted_to_string : 1;
+
+    /* Whether the argument is a string with intervals.  */
     bool_bf intervals : 1;
   } *info;
 
   CHECK_STRING (args[0]);
   char *format_start = SSDATA (args[0]);
+  bool multibyte_format = STRING_MULTIBYTE (args[0]);
   ptrdiff_t formatlen = SBYTES (args[0]);
 
-  /* The number of percent characters is a safe upper bound for the
-     number of format fields.  */
-  ptrdiff_t num_percent = 0;
-  for (ptrdiff_t i = 0; i < formatlen; ++i)
-    if (format_start[i] == '%')
-      ++num_percent;
+  /* Upper bound on number of format specs.  Each uses at least 2 chars.  */
+  ptrdiff_t nspec_bound = SCHARS (args[0]) >> 1;
 
   /* Allocate the info and discarded tables.  */
   ptrdiff_t alloca_size;
-  if (INT_MULTIPLY_WRAPV (num_percent, sizeof *info, &alloca_size)
-      || INT_ADD_WRAPV (sizeof *info, alloca_size, &alloca_size)
+  if (INT_MULTIPLY_WRAPV (nspec_bound, sizeof *info, &alloca_size)
       || INT_ADD_WRAPV (formatlen, alloca_size, &alloca_size)
       || SIZE_MAX < alloca_size)
     memory_full (SIZE_MAX);
-  /* info[0] is unused.  Unused elements have -1 for start.  */
   info = SAFE_ALLOCA (alloca_size);
-  memset (info, 0, alloca_size);
-  for (ptrdiff_t i = 0; i < num_percent + 1; i++)
-    {
-      info[i].argument = Qunbound;
-      info[i].start = -1;
-    }
   /* discarded[I] is 1 if byte I of the format
      string was not copied into the output.
      It is 2 if byte I was not the first byte of its character.  */
-  char *discarded = (char *) &info[num_percent + 1];
+  char *discarded = (char *) &info[nspec_bound];
+  memset (discarded, 0, formatlen);
 
   /* Try to determine whether the result should be multibyte.
      This is not always right; sometimes the result needs to be multibyte
@@ -4030,8 +4020,6 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
      or because a grave accent or apostrophe is requoted,
      and in that case, we won't know it here.  */
 
-  /* True if the format is multibyte.  */
-  bool multibyte_format = STRING_MULTIBYTE (args[0]);
   /* True if the output should be a multibyte string,
      which is true if any of the inputs is one.  */
   bool multibyte = multibyte_format;
@@ -4042,6 +4030,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
   int quoting_style = message ? text_quoting_style () : -1;
 
   ptrdiff_t ispec;
+  ptrdiff_t nspec = 0;
 
   /* If we start out planning a unibyte result,
      then discover it has to be multibyte, we jump back to retry.  */
@@ -4155,11 +4144,14 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
           if (! (n < nargs))
             error ("Not enough arguments for format string");
 
-          eassert (ispec < num_percent);
-          ++ispec;
-
-          if (EQ (info[ispec].argument, Qunbound))
-            info[ispec].argument = args[n];
+          struct info *spec = &info[ispec++];
+          if (nspec < ispec)
+            {
+              spec->argument = args[n];
+              spec->intervals = false;
+              nspec = ispec;
+            }
+          Lisp_Object arg = spec->argument;
 
           /* For 'S', prin1 the argument, and then treat like 's'.
              For 's', princ any argument that is not a string or
@@ -4167,16 +4159,13 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
              happen after retrying.  */
           if ((conversion == 'S'
                || (conversion == 's'
-                   && ! STRINGP (info[ispec].argument)
-                   && ! SYMBOLP (info[ispec].argument))))
+                   && ! STRINGP (arg) && ! SYMBOLP (arg))))
             {
-              if (! info[ispec].converted_to_string)
+              if (EQ (arg, args[n]))
                 {
                   Lisp_Object noescape = conversion == 'S' ? Qnil : Qt;
-                  info[ispec].argument =
-                    Fprin1_to_string (info[ispec].argument, noescape);
-                  info[ispec].converted_to_string = true;
-                  if (STRING_MULTIBYTE (info[ispec].argument) && ! multibyte)
+                  spec->argument = arg = Fprin1_to_string (arg, noescape);
+                  if (STRING_MULTIBYTE (arg) && ! multibyte)
                     {
                       multibyte = true;
                       goto retry;
@@ -4186,29 +4175,25 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
             }
           else if (conversion == 'c')
             {
-              if (INTEGERP (info[ispec].argument)
-                  && ! ASCII_CHAR_P (XINT (info[ispec].argument)))
+              if (INTEGERP (arg) && ! ASCII_CHAR_P (XINT (arg)))
                 {
                   if (!multibyte)
                     {
                       multibyte = true;
                       goto retry;
                     }
-                  info[ispec].argument =
-                    Fchar_to_string (info[ispec].argument);
-                  info[ispec].converted_to_string = true;
+                  spec->argument = arg = Fchar_to_string (arg);
                 }
 
-              if (info[ispec].converted_to_string)
+              if (!EQ (arg, args[n]))
                 conversion = 's';
               zero_flag = false;
             }
 
-          if (SYMBOLP (info[ispec].argument))
+          if (SYMBOLP (arg))
             {
-              info[ispec].argument =
-                SYMBOL_NAME (info[ispec].argument);
-              if (STRING_MULTIBYTE (info[ispec].argument) && ! multibyte)
+              spec->argument = arg = SYMBOL_NAME (arg);
+              if (STRING_MULTIBYTE (arg) && ! multibyte)
                 {
                   multibyte = true;
                   goto retry;
@@ -4239,12 +4224,11 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
               else
                 {
                   ptrdiff_t nch, nby;
-                  width = lisp_string_width (info[ispec].argument,
-                                             prec, &nch, &nby);
+                  width = lisp_string_width (arg, prec, &nch, &nby);
                   if (prec < 0)
                     {
-                      nchars_string = SCHARS (info[ispec].argument);
-                      nbytes = SBYTES (info[ispec].argument);
+                      nchars_string = SCHARS (arg);
+                      nbytes = SBYTES (arg);
                     }
                   else
                     {
@@ -4254,11 +4238,8 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                 }
 
               convbytes = nbytes;
-              if (convbytes && multibyte &&
-                  ! STRING_MULTIBYTE (info[ispec].argument))
-                convbytes =
-                  count_size_as_multibyte (SDATA (info[ispec].argument),
-                                           nbytes);
+              if (convbytes && multibyte && ! STRING_MULTIBYTE (arg))
+                convbytes = count_size_as_multibyte (SDATA (arg), nbytes);
 
               ptrdiff_t padding
                 = width < field_width ? field_width - width : 0;
@@ -4274,20 +4255,18 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                       p += padding;
                       nchars += padding;
                     }
-                  info[ispec].start = nchars;
+                  spec->start = nchars;
 
                   if (p > buf
                       && multibyte
                       && !ASCII_CHAR_P (*((unsigned char *) p - 1))
-                      && STRING_MULTIBYTE (info[ispec].argument)
-                      && !CHAR_HEAD_P (SREF (info[ispec].argument, 0)))
+                      && STRING_MULTIBYTE (arg)
+                      && !CHAR_HEAD_P (SREF (arg, 0)))
                     maybe_combine_byte = true;
 
-                  p += copy_text (SDATA (info[ispec].argument),
-                                  (unsigned char *) p,
+                  p += copy_text (SDATA (arg), (unsigned char *) p,
                                   nbytes,
-                                  STRING_MULTIBYTE (info[ispec].argument),
-                                  multibyte);
+                                  STRING_MULTIBYTE (arg), multibyte);
 
                   nchars += nchars_string;
 
@@ -4297,12 +4276,12 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                       p += padding;
                       nchars += padding;
                     }
-                  info[ispec].end = nchars;
+                  spec->end = nchars;
 
                   /* If this argument has text properties, record where
                      in the result string it appears.  */
-                  if (string_intervals (info[ispec].argument))
-                    info[ispec].intervals = arg_intervals = true;
+                  if (string_intervals (arg))
+                    spec->intervals = arg_intervals = true;
 
                   continue;
                 }
@@ -4313,8 +4292,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                       || conversion == 'X'))
             error ("Invalid format operation %%%c",
                    STRING_CHAR ((unsigned char *) format - 1));
-          else if (! (INTEGERP (info[ispec].argument)
-                      || (FLOATP (info[ispec].argument) && conversion != 'c')))
+          else if (! (INTEGERP (arg) || (FLOATP (arg) && conversion != 'c')))
             error ("Format specifier doesn't match argument type");
           else
             {
@@ -4376,7 +4354,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                     if (INT_AS_LDBL)
                       {
                         *f = 'L';
-                        f += INTEGERP (info[ispec].argument);
+                        f += INTEGERP (arg);
                       }
                   }
                 else if (conversion != 'c')
@@ -4408,22 +4386,22 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
               ptrdiff_t sprintf_bytes;
               if (float_conversion)
                 {
-                  if (INT_AS_LDBL && INTEGERP (info[ispec].argument))
+                  if (INT_AS_LDBL && INTEGERP (arg))
                     {
                       /* Although long double may have a rounding error if
                          DIG_BITS_LBOUND * LDBL_MANT_DIG < FIXNUM_BITS - 1,
                          it is more accurate than plain 'double'.  */
-                      long double x = XINT (info[ispec].argument);
+                      long double x = XINT (arg);
                       sprintf_bytes = sprintf (sprintf_buf, convspec, prec, x);
                     }
                   else
                     sprintf_bytes = sprintf (sprintf_buf, convspec, prec,
-                                             XFLOATINT (info[ispec].argument));
+                                             XFLOATINT (arg));
                 }
               else if (conversion == 'c')
                 {
                   /* Don't use sprintf here, as it might mishandle prec.  */
-                  sprintf_buf[0] = XINT (info[ispec].argument);
+                  sprintf_buf[0] = XINT (arg);
                   sprintf_bytes = prec != 0;
                 }
               else if (conversion == 'd' || conversion == 'i')
@@ -4432,11 +4410,11 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                      instead so it also works for values outside
                      the integer range.  */
                   printmax_t x;
-                  if (INTEGERP (info[ispec].argument))
-                    x = XINT (info[ispec].argument);
+                  if (INTEGERP (arg))
+                    x = XINT (arg);
                   else
                     {
-                      double d = XFLOAT_DATA (info[ispec].argument);
+                      double d = XFLOAT_DATA (arg);
                       if (d < 0)
                         {
                           x = TYPE_MINIMUM (printmax_t);
@@ -4456,11 +4434,11 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                 {
                   /* Don't sign-extend for octal or hex printing.  */
                   uprintmax_t x;
-                  if (INTEGERP (info[ispec].argument))
-                    x = XUINT (info[ispec].argument);
+                  if (INTEGERP (arg))
+                    x = XUINT (arg);
                   else
                     {
-                      double d = XFLOAT_DATA (info[ispec].argument);
+                      double d = XFLOAT_DATA (arg);
                       if (d < 0)
                         x = 0;
                       else
@@ -4541,7 +4519,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                         exponent_bytes = src + sprintf_bytes - e;
                     }
 
-                  info[ispec].start = nchars;
+                  spec->start = nchars;
                   if (! minus_flag)
                     {
                       memset (p, ' ', padding);
@@ -4572,7 +4550,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                       p += padding;
                       nchars += padding;
                     }
-                  info[ispec].end = nchars;
+                  spec->end = nchars;
 
                   continue;
                 }
@@ -4681,7 +4659,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
       if (CONSP (props))
         {
           ptrdiff_t bytepos = 0, position = 0, translated = 0;
-          ptrdiff_t fieldn = 1;
+          ptrdiff_t fieldn = 0;
 
           /* Adjust the bounds of each text property
              to the proper start and end in the output string.  */
@@ -4747,7 +4725,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
 
       /* Add text properties from arguments.  */
       if (arg_intervals)
-        for (ptrdiff_t i = 1; i <= num_percent; i++)
+        for (ptrdiff_t i = 0; i < nspec; i++)
           if (info[i].intervals)
             {
               len = make_number (SCHARS (info[i].argument));