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Avoid shift equal to bits in type (caused endless loop).

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Also clean up comparisons between different types, and some odd
indentation problems that showed up somehow.

A new endless loop was introduced by the clang compiler, which
apparently does odd things when the right operand of << is equal to
or greater than the number of bits in the type.  The C standard in
fact states that the behavior of << is undefined in that case.  The
loop was rewritten to use single-bit shifts.
This commit is contained in:
Mark Adler 2012-08-18 17:59:50 -07:00
parent 3d9df6ecf8
commit 17068938ce
1 changed files with 21 additions and 18 deletions
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25
examples/enough.c
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@ -1,7 +1,7 @@
/* enough.c -- determine the maximum size of inflate's Huffman code tables over
* all possible valid and complete Huffman codes, subject to a length limit.
* Copyright (C) 2007, 2008 Mark Adler
* Version 1.3 17 February 2008 Mark Adler
* Copyright (C) 2007, 2008, 2012 Mark Adler
* Version 1.4 18 August 2012 Mark Adler
*/
/* Version history:
@ -14,6 +14,9 @@
1.3 17 Feb 2008 Add argument for initial root table size
Fix bug for initial root table size == max - 1
Use a macro to compute the history index
1.4 18 Aug 2012 Avoid shifts more than bits in type (caused endless loop!)
Clean up comparisons of different types
Clean up code indentation
*/
/*
@ -236,8 +239,8 @@ local big_t count(int syms, int len, int left)
for (use = least; use <= most; use++) {
got = count(syms - use, len + 1, (left - use) << 1);
sum += got;
if (got == -1 || sum < got) /* overflow */
return -1;
if (got == (big_t)0 - 1 || sum < got) /* overflow */
return (big_t)0 - 1;
}
/* verify that all recursive calls are productive */
@ -458,6 +461,7 @@ int main(int argc, char **argv)
int n; /* number of symbols to code for this run */
big_t got; /* return value of count() */
big_t sum; /* accumulated number of codes over n */
code_t word; /* for counting bits in code_t */
/* set up globals for cleanup() */
code = NULL;
@ -487,18 +491,17 @@ int main(int argc, char **argv)
max = syms - 1;
/* determine the number of bits in a code_t */
n = 0;
while (((code_t)1 << n) != 0)
n++;
for (n = 0, word = 1; word; n++, word <<= 1)
;
/* make sure that the calculation of most will not overflow */
if (max > n || syms - 2 >= (((code_t)0 - 1) >> (max - 1))) {
if (max > n || (code_t)(syms - 2) >= (((code_t)0 - 1) >> (max - 1))) {
fputs("abort: code length too long for internal types\n", stderr);
return 1;
}
/* reject impossible code requests */
if (syms - 1 > ((code_t)1 << max) - 1) {
if ((code_t)(syms - 1) > ((code_t)1 << max) - 1) {
fprintf(stderr, "%d symbols cannot be coded in %d bits\n",
syms, max);
return 1;
@ -532,7 +535,7 @@ int main(int argc, char **argv)
for (n = 2; n <= syms; n++) {
got = count(n, 1, 2);
sum += got;
if (got == -1 || sum < got) { /* overflow */
if (got == (big_t)0 - 1 || sum < got) { /* overflow */
fputs("abort: can't count that high!\n", stderr);
cleanup();
return 1;
@ -558,7 +561,7 @@ int main(int argc, char **argv)
/* find and show maximum inflate table usage */
if (root > max) /* reduce root to max length */
root = max;
if (syms < ((code_t)1 << (root + 1)))
if ((code_t)syms < ((code_t)1 << (root + 1)))
enough(syms);
else
puts("cannot handle minimum code lengths > root");