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Streamline styled_format aux allocation

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* src/editfns.c (styled_format): Streamline allocation of
auxiliary tables, by allocating them all in one go
rather than via separate alloca / mallocs.
This commit is contained in:
Paul Eggert 2026-05-16 23:30:53 -07:00
parent 84e646f0b3
commit 1fae14a022
1 changed files with 20 additions and 15 deletions
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35
src/editfns.c
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@ -3490,29 +3490,34 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
CHECK_STRING (args[0]);
bool multibyte_format = STRING_MULTIBYTE (args[0]);
ptrdiff_t formatlen = SBYTES (args[0]);
char *format_start = SAFE_ALLOCA (formatlen + 1);
memcpy (format_start, SSDATA (args[0]), formatlen + 1);
bool fmt_props = !!string_intervals (args[0]);
/* 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 info_size, alloca_size;
if (ckd_mul (&info_size, nspec_bound, sizeof *info)
|| ckd_add (&alloca_size, formatlen, info_size)
|| SIZE_MAX < alloca_size)
/* Allocate auxiliary tables in one go, in the order:
spec_arguments, info, format_start, discarded.
Because nspec_bound <= formatlen / 2, EXTRA is an upper bound on
(nspec_bound * sizeof *info {for info} + formatlen {for
format_start} + formatlen {for discarded}). */
ptrdiff_t extra;
if (ckd_mul (&extra, formatlen, 2 + (sizeof *info + 1) / 2))
memory_full (SIZE_MAX);
info = SAFE_ALLOCA (alloca_size);
/* One argument belonging to each spec; but needs to be allocated
separately so GC doesn't free the strings (bug#75754). */
Lisp_Object *spec_arguments;
SAFE_ALLOCA_LISP (spec_arguments, nspec_bound);
/* 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[nspec_bound];
memset (discarded, 0, formatlen);
SAFE_ALLOCA_LISP_EXTRA (spec_arguments, nspec_bound, extra);
/* The info table. */
static_assert (alignof (struct info) <= alignof (Lisp_Object));
info = (struct info *) &spec_arguments[nspec_bound];
/* The format string's bytes, sans trailing '\0'. */
char *format_start = memcpy (&info[nspec_bound],
SSDATA (args[0]), formatlen);
/* discarded[I] is:
1 if byte I of the format string was not copied into the output.
2 if byte I was not the first byte of its character.
0 otherwise. */
char *discarded = memset (&format_start[formatlen], 0, formatlen);
/* Try to determine whether the result should be multibyte.
This is not always right; sometimes the result needs to be multibyte
@ -4397,7 +4402,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
}
return_val:
/* If we allocated BUF or INFO with malloc, free it too. */
/* If we allocated BUF or auxiliary tables with malloc, free it too. */
SAFE_FREE ();
return val;