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stb_image: Avoid shift of signed values in extend_receive

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Use an equivalent formulation that has sgn=0 or 1, not 0 or -1.
This avoids right-shifting signed values, at least in this place.

Fixes issue #1061.
This commit is contained in:
Fabian Giesen 2021-07-02 20:59:22 -07:00
parent 6d857933d5
commit 43b32c7bab
1 changed files with 2 additions and 2 deletions
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4
stb_image.h
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@ -2102,12 +2102,12 @@ stbi_inline static int stbi__extend_receive(stbi__jpeg *j, int n)
int sgn; int sgn;
if (j->code_bits < n) stbi__grow_buffer_unsafe(j); if (j->code_bits < n) stbi__grow_buffer_unsafe(j);
sgn = (stbi__int32)j->code_buffer >> 31; // sign bit is always in MSB sgn = j->code_buffer >> 31; // sign bit always in MSB; 0 if MSB clear (positive), 1 if MSB set (negative)
k = stbi_lrot(j->code_buffer, n); k = stbi_lrot(j->code_buffer, n);
j->code_buffer = k & ~stbi__bmask[n]; j->code_buffer = k & ~stbi__bmask[n];
k &= stbi__bmask[n]; k &= stbi__bmask[n];
j->code_bits -= n; j->code_bits -= n;
return k + (stbi__jbias[n] & ~sgn); return k + (stbi__jbias[n] & (sgn - 1));
} }
// get some unsigned bits // get some unsigned bits