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#440: fix end-of-string bug with vmx_strchr()

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This commit is contained in:
Cameron Kaiser 2017-11-16 17:24:36 -08:00
parent c0b52e0122
commit f6c2519506
1 changed files with 65 additions and 1 deletions
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66
nsprpub/lib/libc/src/plvmx.c
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@ -118,6 +118,8 @@ foundResult:
return NULL;
}
/* The below is (C)2017 Cameron Kaiser. All rights reserved. */
char *vmx_strchr(const char *p, int ch) {
unsigned char c = (unsigned char)ch;
unsigned int val;
@ -135,13 +137,26 @@ char *vmx_strchr(const char *p, int ch) {
mashedByte, mashedByte, mashedByte, mashedByte};
const vector unsigned char nullVector = vec_splat_u8(0);
// We can get away with this because OS X guarantees to always
// malloc at least 16 bytes on AltiVec-capable systems, and stack
// allocations will never end up in unmapped memory.
const vector unsigned char *w;
for(; ; p+=16) {
const vector unsigned char *w = (const vector unsigned char*)p;
w = (const vector unsigned char*)p;
if (vec_any_eq(*w, searchVector)) break;
if (vec_any_eq(*w, nullVector)) return NULL;
}
// Some byte has the result; look in groups of 4 to find which one.
// It is possible if we're looking at a batch of 16 bytes near
// the end of the string that there is both the search byte and
// the null, but the null precedes it (i.e., the search byte is in
// some block of garbage memory at the end). AltiVec can't tell us
// where the bytes are, but if there's no null at all, we don't need
// to check further for one.
if (vec_any_eq(*w, nullVector)) goto thereisanull;
// No null is present.
// Unroll the loop.
val = *(unsigned int*)p;
if (((val >> 24) & 0xFF) == c) return (void *)p;
@ -166,6 +181,55 @@ char *vmx_strchr(const char *p, int ch) {
if (((val >> 16) & 0xFF) == c) return (void *)(1 + p);
if (((val >> 8) & 0xFF) == c) return (void *)(2 + p);
if ((val & 0xFF) == c) return (void *)(3 + p);
goto wtf;
thereisanull:
;
// A null is present. Check string termination at each
// character position. Unroll the loop.
val = *(unsigned int*)p;
if (((val >> 24) & 0xFF) == c) return (void *)p;
if (((val >> 24) & 0xFF) == 0) return NULL;
if (((val >> 16) & 0xFF) == c) return (void *)(1 + p);
if (((val >> 16) & 0xFF) == 0) return NULL;
if (((val >> 8) & 0xFF) == c) return (void *)(2 + p);
if (((val >> 8) & 0xFF) == 0) return NULL;
if ((val & 0xFF) == c) return (void *)(3 + p);
if ((val & 0xFF) == 0) return NULL;
p += 4;
val = *(unsigned int*)p;
if (((val >> 24) & 0xFF) == c) return (void *)p;
if (((val >> 24) & 0xFF) == 0) return NULL;
if (((val >> 16) & 0xFF) == c) return (void *)(1 + p);
if (((val >> 16) & 0xFF) == 0) return NULL;
if (((val >> 8) & 0xFF) == c) return (void *)(2 + p);
if (((val >> 8) & 0xFF) == 0) return NULL;
if ((val & 0xFF) == c) return (void *)(3 + p);
if ((val & 0xFF) == 0) return NULL;
p += 4;
val = *(unsigned int*)p;
if (((val >> 24) & 0xFF) == c) return (void *)p;
if (((val >> 24) & 0xFF) == 0) return NULL;
if (((val >> 16) & 0xFF) == c) return (void *)(1 + p);
if (((val >> 16) & 0xFF) == 0) return NULL;
if (((val >> 8) & 0xFF) == c) return (void *)(2 + p);
if (((val >> 8) & 0xFF) == 0) return NULL;
if ((val & 0xFF) == c) return (void *)(3 + p);
if ((val & 0xFF) == 0) return NULL;
p += 4;
val = *(unsigned int*)p;
if (((val >> 24) & 0xFF) == c) return (void *)p;
if (((val >> 24) & 0xFF) == 0) return NULL;
if (((val >> 16) & 0xFF) == c) return (void *)(1 + p);
if (((val >> 16) & 0xFF) == 0) return NULL;
if (((val >> 8) & 0xFF) == c) return (void *)(2 + p);
if (((val >> 8) & 0xFF) == 0) return NULL;
if ((val & 0xFF) == c) return (void *)(3 + p);
if ((val & 0xFF) == 0) return NULL;
wtf:
;
// unreachable
fprintf(stderr, "failed vmx_strchr()\n");