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mruby-sprintf: optimize %c to avoid temporary string allocation

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For integer arguments, encode UTF-8 directly into a stack buffer
instead of creating a temporary mrb_value string via mrb_str_new()
or calling Integer#chr.

- ~5% faster for single %c
- ~15% faster for multiple %c in one format string
- fixes UTF-8 characters (>= 0x80) which previously raised RangeError

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-12-18 16:15:52 +09:00
parent baff6e630a
commit 53fce124e6
1 changed files with 44 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files
mrbgems/mruby-sprintf/src/sprintf.c
+44 -30
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@@ -512,42 +512,57 @@ retry:
case FMT_CHAR: {
/* CHARACTER FORMATTING (%c) */
mrb_value val = GETARG();
mrb_value tmp;
char *c;
const char *c;
char cbuf[4]; /* stack buffer for character bytes */
int clen;
/* Convert argument to character string */
tmp = mrb_check_string_type(mrb, val);
if (!mrb_nil_p(tmp)) {
if (mrb_integer_p(val)) {
/* Integer: encode directly to stack buffer (no allocation) */
mrb_int code = mrb_integer(val);
#ifdef MRB_UTF8_STRING
if (code < 0x80) {
cbuf[0] = (char)code;
clen = 1;
}
else if (code < 0x800) {
cbuf[0] = (char)(0xC0 | (code >> 6));
cbuf[1] = (char)(0x80 | (code & 0x3F));
clen = 2;
}
else if (code < 0x10000) {
cbuf[0] = (char)(0xE0 | (code >> 12));
cbuf[1] = (char)(0x80 | ((code >> 6) & 0x3F));
cbuf[2] = (char)(0x80 | (code & 0x3F));
clen = 3;
}
else {
cbuf[0] = (char)(0xF0 | (code >> 18));
cbuf[1] = (char)(0x80 | ((code >> 12) & 0x3F));
cbuf[2] = (char)(0x80 | ((code >> 6) & 0x3F));
cbuf[3] = (char)(0x80 | (code & 0x3F));
clen = 4;
}
#else
cbuf[0] = (char)(code & 0xff);
clen = 1;
#endif
c = cbuf;
}
else {
/* String: validate and use directly */
mrb_value tmp = mrb_check_string_type(mrb, val);
if (mrb_nil_p(tmp)) {
mrb_raise(mrb, E_ARGUMENT_ERROR, "invalid character");
}
if (RSTRING_LEN(tmp) != 1) {
mrb_raise(mrb, E_ARGUMENT_ERROR, "%c requires a character");
}
c = RSTRING_PTR(tmp);
clen = (int)RSTRING_LEN(tmp);
}
else if (mrb_integer_p(val)) {
mrb_int n = mrb_integer(val);
#ifndef MRB_UTF8_STRING
char buf[1];
buf[0] = (char)n&0xff;
tmp = mrb_str_new(mrb, buf, 1);
#else
if (n < 0x80) {
char buf[1];
buf[0] = (char)n;
tmp = mrb_str_new(mrb, buf, 1);
}
else {
tmp = mrb_funcall_argv(mrb, val, MRB_SYM(chr), 0, NULL);
mrb_check_type(mrb, tmp, MRB_TT_STRING);
}
#endif
}
else {
mrb_raise(mrb, E_ARGUMENT_ERROR, "invalid character");
}
/* Format and output the character with width/alignment */
c = RSTRING_PTR(tmp);
n = (int)RSTRING_LEN(tmp);
n = clen;
if (!(flags & FWIDTH)) {
PUSH(c, n);
}
@@ -559,7 +574,6 @@ retry:
if (width>0) FILL(' ', width-1);
PUSH(c, n);
}
mrb_gc_arena_restore(mrb, ai);
}
break;