[BusyBox] [patch] micro-bunzip version 3. :)
Manuel Novoa III
mjn3 at codepoet.org
Fri Oct 17 03:01:52 UTC 2003
Hello Rob,
Here's a patch to your bunzip-3.c file. Nice work btw.
One minor bug fix... checking for error return when read()ing.
Some size/performance optimizations as well. One instance of
memset() seems unnecssary. You might want to take a look.
Anyway, on my machine, decompressing linux-2.6.0-test7.tar.bz2
to /dev/null gave the following times:
bunzip-3.c bzcat (system) bunzip-3.c (patched)
real 0m24.420s 0m22.725s 0m20.701s
user 0m23.930s 0m22.170s 0m20.180s
sys 0m0.070s 0m0.080s 0m0.140s
Size of the patched version is comparable (slightly larger or
smaller depending on compiler flags).
Manuel
-------------- next part --------------
--- bunzip-3-dist.c 2003-10-16 08:28:18.000000000 -0500
+++ bunzip-3-new.c 2003-10-16 21:39:57.000000000 -0500
@@ -17,6 +17,7 @@
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
+#include <limits.h>
/* Constants for huffman coding */
#define MAX_GROUPS 6
@@ -39,13 +40,14 @@
/* Other housekeeping constants */
#define IOBUF_SIZE 4096
-char *bunzip_errors[]={NULL,"Bad file checksum","Not bzip data",
+static char * const bunzip_errors[]={NULL,"Bad file checksum","Not bzip data",
"Unexpected input EOF","Unexpected output EOF","Data error",
"Out of memory","Obsolete (pre 0.9.5) bzip format not supported."};
/* 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];
+ /* We have an extra slot at the end of limit[] for a sentinal value. */
+ int limit[MAX_HUFCODE_BITS+1],base[MAX_HUFCODE_BITS],permute[MAX_SYMBOLS];
char minLen, maxLen;
};
@@ -84,7 +86,7 @@
while (bd->inbufBitCount<bits_wanted) {
/* If we need to read more data from file into byte buffer, do so */
if(bd->inbufPos==bd->inbufCount) {
- if(!(bd->inbufCount = read(bd->in_fd, bd->inbuf, IOBUF_SIZE)))
+ if((bd->inbufCount = read(bd->in_fd, bd->inbuf, IOBUF_SIZE)) <= 0)
longjmp(bd->jmpbuf,RETVAL_UNEXPECTED_INPUT_EOF);
bd->inbufPos=0;
}
@@ -106,6 +108,14 @@
return bits;
}
+/* At certain times, it pays to have an optimized inline version of
+ * get_bits() which gets a single bit. */
+#define GET_A_BIT(bd) \
+ ((bd->inbufBitCount > 0) \
+ ? ((unsigned int)(((bd)->inbufBits >> --(bd)->inbufBitCount) & 1)) \
+ : get_bits((bd), 1))
+
+
/* Decompress a block of text to into intermediate buffer */
extern int read_bunzip_data(bunzip_data *bd)
@@ -142,7 +152,10 @@
values were present. We make a translation table to convert the symbols
back to the corresponding bytes. */
t=get_bits(bd, 16);
+#if 0
+ /* I don't believe this is necessary. Rob? */
memset(symToByte,0,256);
+#endif
symTotal=0;
for (i=0;i<16;i++) {
if(t&(1<<(15-i))) {
@@ -164,7 +177,13 @@
for(j=0;get_bits(bd,1);j++) if (j>=groupCount) return RETVAL_DATA_ERROR;
/* Decode MTF to get the next selector */
uc = mtfSymbol[j];
- memmove(mtfSymbol+1,mtfSymbol,j);
+ /* A very small amount of data to move, so memmove is overkill
+ * and bigger at least in my tests. */
+ k = j;
+ while (k) {
+ mtfSymbol[k] = mtfSymbol[k-1];
+ --k;
+ }
mtfSymbol[0]=selectors[i]=uc;
}
/* Read the huffman coding tables for each group, which code for symTotal
@@ -174,15 +193,15 @@
unsigned char length[MAX_SYMBOLS],temp[MAX_HUFCODE_BITS+1];
int minLen, maxLen, pp;
/* Read lengths */
- t=get_bits(bd, 5);
+ t=get_bits(bd, 5) - 1; /* This lets us avoid a test in the loop. */
for (i = 0; i < symCount; i++) {
for(;;) {
- if (t < 1 || t > MAX_HUFCODE_BITS) return RETVAL_DATA_ERROR;
+ if (((unsigned)t) > (MAX_HUFCODE_BITS-1)) return RETVAL_DATA_ERROR;
if(!get_bits(bd, 1)) break;
- if(!get_bits(bd, 1)) t++;
- else t--;
+ /* We can avoid an if/else with a little arithmetic. */
+ t += (1 - 2*get_bits(bd, 1)); /* 0 -> t++ ; 1 -> t-- */
}
- length[i] = t;
+ length[i] = t + 1; /* Correct for the initial -1 adjustment. */
}
/* Find largest and smallest lengths in this group */
minLen=maxLen=length[0];
@@ -230,6 +249,7 @@
pp<<=1;
base[i+1]=pp-(t+=temp[i]);
}
+ limit[maxLen+1] = INT_MAX; /* Sentinal value for reading next sym. */
limit[maxLen]=pp+temp[maxLen]-1;
base[minLen]=0;
}
@@ -254,19 +274,15 @@
/* 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;
- i++;
-
- j = (j << 1) | get_bits(bd,1);
+ while (j > limit[i]) { /* The sentinal allows us to avoid testing i. */
+ j = (j << 1) | GET_A_BIT(bd);
+ ++i;
}
/* 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-=base[i])) >= MAX_SYMBOLS)) return RETVAL_DATA_ERROR;
nextSym = hufGroup->permute[j];
/* If this is a repeated run, loop collecting data */
- if (nextSym == SYMBOL_RUNA || nextSym == SYMBOL_RUNB) {
+ if (((unsigned)nextSym) <= SYMBOL_RUNB) { /* RUNA or RUNB */
/* If this is the start of a new run, zero out counter */
if(!runPos) {
runPos = 1;
@@ -279,8 +295,7 @@
the basic or 0/1 method (except all bits 0, which would use no
symbols, but a run of length 0 doesn't mean anything in this
context). Thus space is saved. */
- if (nextSym == SYMBOL_RUNA) t += runPos;
- else t += 2*runPos;
+ t += (runPos << nextSym); /* +runPos if RUNA; +2*runPos if RUNB */
runPos <<= 1;
continue;
}
@@ -307,7 +322,13 @@
if(dbufCount>=dbufSize) return RETVAL_DATA_ERROR;
i = nextSym - 1;
uc = mtfSymbol[i];
- memmove(mtfSymbol+1,mtfSymbol,i);
+ /* Since we typically expect to move only a small number of symbols,
+ * and are bound by 256 in any case, using memmove here would
+ * typically be slower due to function call overhead and other
+ * assorted setup costs. */
+ do {
+ mtfSymbol[i] = mtfSymbol[i-1];
+ } while (--i);
mtfSymbol[0] = uc;
uc=symToByte[uc];
/* We have our literal byte. Save it into dbuf. */
@@ -321,7 +342,7 @@
*/
/* Now we know what dbufCount is, do a better sanity check on origPtr. */
- if (origPtr<0 || origPtr>=dbufCount) return RETVAL_DATA_ERROR;
+ if (((unsigned)origPtr)>=dbufCount) return RETVAL_DATA_ERROR;
/* Turn byteCount into cumulative occurrence counts of 0 to n-1. */
j=0;
for(i=0;i<256;i++) {
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