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stb_image: Fix lrot definition, small extend_receive tweak 

Define lrot in a way that doesn't involve UB when n==0.
Also, the previous patch ensures that n <= 15 for all callers
of stbi__extend_receive, so can remove the (less restrictive)
bounds check for 0 <= n < 17 (the bounds of stbi__bmask)
entirely.

Fixes issue #1065.
This commit is contained in:
Fabian Giesen 2021-07-02 18:28:41 -07:00
parent a3f2897b85
commit 1d7bf85877
1 changed files with 1 additions and 2 deletions
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stb_image.h
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@ -645,7 +645,7 @@ typedef unsigned char validate_uint32[sizeof(stbi__uint32)==4 ? 1 : -1];
#ifdef STBI_HAS_LROTL
#define stbi_lrot(x,y) _lrotl(x,y)
#else
#define stbi_lrot(x,y) (((x) << (y)) | ((x) >> (32 - (y))))
#define stbi_lrot(x,y) (((x) << (y)) | ((x) >> (-(y) & 31)))
#endif
#if defined(STBI_MALLOC) && defined(STBI_FREE) && (defined(STBI_REALLOC) || defined(STBI_REALLOC_SIZED))
@ -2104,7 +2104,6 @@ stbi_inline static int stbi__extend_receive(stbi__jpeg *j, int n)
sgn = (stbi__int32)j->code_buffer >> 31; // sign bit is always in MSB
k = stbi_lrot(j->code_buffer, n);
if (n < 0 || n >= (int) (sizeof(stbi__bmask)/sizeof(*stbi__bmask))) return 0;
j->code_buffer = k & ~stbi__bmask[n];
k &= stbi__bmask[n];
j->code_bits -= n;