More optimizations originally suggested by Manuel Nova: Use a sentinel value
for limit[] to move a test out of a loop. Unroll a single-bit get_bits()
to avoid a function call in the common case on a hot path. And one more
application of the old "two tests in one via typecasting and/or math" trick.
diff --git a/lib/bunzip.c b/lib/bunzip.c
index c1020ee..a69e618 100644
--- a/lib/bunzip.c
+++ b/lib/bunzip.c
@@ -46,7 +46,7 @@
// This is what we know about each huffman coding group
struct group_data {
- int limit[MAX_HUFCODE_BITS], base[MAX_HUFCODE_BITS], permute[MAX_SYMBOLS];
+ int limit[MAX_HUFCODE_BITS+1], base[MAX_HUFCODE_BITS], permute[MAX_SYMBOLS];
char minLen, maxLen;
};
@@ -259,6 +259,7 @@
base[i+1] = pp-(t+=temp[i]);
}
limit[maxLen] = pp+temp[maxLen]-1;
+ limit[maxLen+1] = INT_MAX;
base[minLen] = 0;
}
@@ -288,17 +289,22 @@
// Read next huffman-coded symbol
i = hufGroup->minLen;
j = get_bits(bd, i);
- for (;;) {
- if (i > hufGroup->maxLen) return RETVAL_DATA_ERROR;
- if (j <= limit[i]) break;
+ while (j > limit[i]) {
+ // if (i > hufGroup->maxLen) return RETVAL_DATA_ERROR;
i++;
- j = (j << 1) | get_bits(bd,1);
+ // Unroll get_bits() to avoid a function call when the data's in
+ // the buffer already.
+ k = bd->inbufBitCount
+ ? (bd->inbufBits >> --(bd->inbufBitCount)) & 1
+ : get_bits(bd, 1);
+ j = (j << 1) | k;
}
// Huffman decode nextSym (with bounds checking)
j-=base[i];
- if (j < 0 || j >= MAX_SYMBOLS) return RETVAL_DATA_ERROR;
+ if (i > hufGroup->maxLen || (unsigned)j >= MAX_SYMBOLS)
+ return RETVAL_DATA_ERROR;
nextSym = hufGroup->permute[j];
// If this is a repeated run, loop collecting data
