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mruby-pack: optimize base64 encoding for memory efficiency

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- add fast path for no line wrapping (count=0) to avoid column tracking
- use precise buffer size calculation to prevent reallocations
- move variable declarations to initialization points for cleaner code
- maintain full backward compatibility

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-08-12 17:19:53 +09:00
parent 64886fd965
commit 2639e9d8cd
1 changed files with 71 additions and 33 deletions
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mrbgems/mruby-pack/src/pack.c
+71 -33
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@@ -954,66 +954,104 @@ unpack_bstr(mrb_state *mrb, const void *src, int slen, mrb_value ary, int count,
static int
pack_base64(mrb_state *mrb, mrb_value src, mrb_value dst, mrb_int didx, int count)
{
mrb_int dstlen;
unsigned long l;
mrb_int column, srclen;
char *srcptr, *dstptr, *dstptr0;
char *srcptr = RSTRING_PTR(src);
mrb_int srclen = RSTRING_LEN(src);
srcptr = RSTRING_PTR(src);
srclen = RSTRING_LEN(src);
if (srclen == 0) /* easy case */
if (srclen == 0) {
return 0;
}
if (count != 0 && count < 3) { /* -1, 1 or 2 */
if (count != 0 && count < 3) {
count = 45;
}
else if (count >= 3) {
count -= count % 3;
}
dstlen = (srclen+2) / 3 * 4;
/* precise memory allocation */
mrb_int dstlen = (srclen + 2) / 3 * 4;
if (count > 0) {
dstlen += (srclen / count) + ((srclen % count) == 0 ? 0 : 1);
}
dst = str_len_ensure(mrb, dst, didx + dstlen);
dstptr = RSTRING_PTR(dst) + didx;
char *dstptr = RSTRING_PTR(dst) + didx;
char *dstptr0 = dstptr;
dstptr0 = dstptr;
for (column = 3; srclen >= 3; srclen -= 3, column += 3) {
l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr++ << 8;
l += (unsigned char)*srcptr++;
if (count == 0) {
/* fast path: no line wrapping */
while (srclen >= 3) {
unsigned long l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr++ << 8;
l += (unsigned char)*srcptr++;
srclen -= 3;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = base64chars[ l & 0x3f];
if (column == count) {
*dstptr++ = '\n';
column = 0;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = base64chars[l & 0x3f];
}
}
else {
/* line wrapping path */
mrb_int column = 3;
while (srclen >= 3) {
unsigned long l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr++ << 8;
l += (unsigned char)*srcptr++;
srclen -= 3;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = base64chars[l & 0x3f];
if (column == count) {
*dstptr++ = '\n';
column = 0;
}
column += 3;
}
/* handle remaining 1-2 bytes */
if (srclen == 1) {
unsigned long l = (unsigned char)*srcptr << 16;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = '=';
*dstptr++ = '=';
column += 3;
}
else if (srclen == 2) {
unsigned long l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr << 8;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = '=';
column += 3;
}
if (column > 0) {
*dstptr++ = '\n';
}
return (int)(dstptr - dstptr0);
}
/* handle remaining 1-2 bytes for fast path */
if (srclen == 1) {
l = (unsigned char)*srcptr++ << 16;
unsigned long l = (unsigned char)*srcptr << 16;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = '=';
*dstptr++ = '=';
column += 3;
}
else if (srclen == 2) {
l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr++ << 8;
unsigned long l = (unsigned char)*srcptr++ << 16;
l += (unsigned char)*srcptr << 8;
*dstptr++ = base64chars[(l >> 18) & 0x3f];
*dstptr++ = base64chars[(l >> 12) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = base64chars[(l >> 6) & 0x3f];
*dstptr++ = '=';
column += 3;
}
if (column > 0 && count > 0) {
*dstptr++ = '\n';
}
return (int)(dstptr - dstptr0);