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 (file)
--- a/lib/bunzip.c
+++ b/lib/bunzip.c
@@ -46,7 +46,7 @@ char *bunzip_errors[]={
 
 // 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 @@ int read_bunzip_data(bunzip_data *bd)
                        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 @@ int read_bunzip_data(bunzip_data *bd)
                // 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