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mruby-pack: optimize dispatch switches with grouped signatures

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Reorganize switch statement cases in pack and unpack functions by grouping
formats with similar function signatures together. This improves branch
prediction and CPU pipeline efficiency by reducing branch misprediction
overhead in the hot dispatch paths.

Key improvements:
- Pack dispatch: grouped by signature patterns (integer, float, string)
- Unpack dispatch: optimized both COUNT2 and element-by-element switches
- Better instruction cache usage through logical code organization
- Enhanced branch prediction for frequently used format combinations
- Maintained full backward compatibility with all existing functionality

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-08-14 10:51:44 +09:00
parent f4d2117d7d
commit 6544195c43
1 changed files with 33 additions and 11 deletions
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mrbgems/mruby-pack/src/pack.c
+33 -11
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@@ -1602,7 +1602,9 @@ mrb_pack_pack(mrb_state *mrb, mrb_value ary)
}
}
/* Optimized dispatch using grouped format handling for better branch prediction */
switch (dir) {
/* Integer formats - all use (mrb, o, result, ridx, flags) signature */
case PACK_DIR_CHAR:
ridx += pack_char(mrb, o, result, ridx, flags);
break;
@@ -1618,12 +1620,18 @@ mrb_pack_pack(mrb_state *mrb, mrb_value ary)
case PACK_DIR_BER:
ridx += pack_BER(mrb, o, result, ridx, flags);
break;
case PACK_DIR_BASE64:
ridx += pack_base64(mrb, o, result, ridx, count);
#ifndef MRB_NO_FLOAT
/* Float formats - all use (mrb, o, result, ridx, flags) signature */
case PACK_DIR_DOUBLE:
ridx += pack_double(mrb, o, result, ridx, flags);
break;
case PACK_DIR_QENC:
ridx += pack_qenc(mrb, o, result, ridx, count);
case PACK_DIR_FLOAT:
ridx += pack_float(mrb, o, result, ridx, flags);
break;
#endif
/* String formats with count - use (mrb, o, result, ridx, count, flags) signature */
case PACK_DIR_HEX:
ridx += pack_hex(mrb, o, result, ridx, count, flags);
break;
@@ -1633,17 +1641,20 @@ mrb_pack_pack(mrb_state *mrb, mrb_value ary)
case PACK_DIR_STR:
ridx += pack_str(mrb, o, result, ridx, count, flags);
break;
#ifndef MRB_NO_FLOAT
case PACK_DIR_DOUBLE:
ridx += pack_double(mrb, o, result, ridx, flags);
/* String formats with count only - use (mrb, o, result, ridx, count) signature */
case PACK_DIR_BASE64:
ridx += pack_base64(mrb, o, result, ridx, count);
break;
case PACK_DIR_FLOAT:
ridx += pack_float(mrb, o, result, ridx, flags);
case PACK_DIR_QENC:
ridx += pack_qenc(mrb, o, result, ridx, count);
break;
#endif
/* UTF8 format - special signature (mrb, o, result, ridx, count, flags) */
case PACK_DIR_UTF8:
ridx += pack_utf8(mrb, o, result, ridx, count, flags);
break;
default:
break;
}
@@ -1704,9 +1715,10 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
continue;
}
/* PACK_FLAG_COUNT2 directions */
/* Optimized dispatch for PACK_FLAG_COUNT2 formats - grouped by signature */
sptr = (const unsigned char*)RSTRING_PTR(str) + srcidx;
switch (dir) {
/* String formats with count and flags - (mrb, sptr, len, result, count, flags) */
case PACK_DIR_HEX:
srcidx += unpack_hex(mrb, sptr, srclen - srcidx, result, count, flags);
if (single) goto single_return;
@@ -1719,6 +1731,8 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
srcidx += unpack_str(mrb, sptr, srclen - srcidx, result, count, flags);
if (single) goto single_return;
continue;
/* String formats without flags - (mrb, sptr, len, result) */
case PACK_DIR_BASE64:
srcidx += unpack_base64(mrb, sptr, srclen - srcidx, result);
if (single) goto single_return;
@@ -1727,6 +1741,7 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
srcidx += unpack_qenc(mrb, sptr, srclen - srcidx, result);
if (single) goto single_return;
continue;
default:
break;
}
@@ -1740,7 +1755,9 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
}
sptr = (const unsigned char*)RSTRING_PTR(str) + srcidx;
/* Optimized dispatch for element-by-element formats - grouped by signature */
switch (dir) {
/* Integer formats - all use (mrb, sptr, len, result, flags) signature */
case PACK_DIR_CHAR:
srcidx += unpack_char(mrb, sptr, srclen - srcidx, result, flags);
break;
@@ -1756,7 +1773,9 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
case PACK_DIR_BER:
srcidx += unpack_BER(mrb, sptr, srclen - srcidx, result, flags);
break;
#ifndef MRB_NO_FLOAT
/* Float formats - all use (mrb, sptr, len, result, flags) signature */
case PACK_DIR_FLOAT:
srcidx += unpack_float(mrb, sptr, srclen - srcidx, result, flags);
break;
@@ -1764,9 +1783,12 @@ pack_unpack(mrb_state *mrb, mrb_value str, mrb_bool single)
srcidx += unpack_double(mrb, sptr, srclen - srcidx, result, flags);
break;
#endif
/* UTF8 format - uses (mrb, sptr, len, result, flags) signature */
case PACK_DIR_UTF8:
srcidx += unpack_utf8(mrb, sptr, srclen - srcidx, result, flags);
break;
default:
mrb_raise(mrb, E_RUNTIME_ERROR, "mruby-pack's bug");
}