Commit 90a109f0 authored by Johann's avatar Johann Committed by Johann Koenig

Restrict get_msb inputs

Add a warning and assert that inputs for get_msb must not be zero.

Change-Id: I8c6f289ff13248f6e3a8bc24aab3712ed33022a6
parent 36c4e8b2
......@@ -11,6 +11,8 @@
#ifndef VPX_PORTS_BITOPS_H_
#define VPX_PORTS_BITOPS_H_
#include <assert.h>
#include "vpx_ports/msvc.h"
#ifdef _MSC_VER
......@@ -25,10 +27,15 @@
extern "C" {
#endif
// These versions of get_msb() are only valid when n != 0 because all
// of the optimized versions are undefined when n == 0:
// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
// use GNU builtins where available.
#if defined(__GNUC__) && \
((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
static INLINE int get_msb(unsigned int n) {
assert(n != 0);
return 31 ^ __builtin_clz(n);
}
#elif defined(USE_MSC_INTRINSICS)
......@@ -36,6 +43,7 @@ static INLINE int get_msb(unsigned int n) {
static INLINE int get_msb(unsigned int n) {
unsigned long first_set_bit;
assert(n != 0);
_BitScanReverse(&first_set_bit, n);
return first_set_bit;
}
......@@ -47,6 +55,8 @@ static INLINE int get_msb(unsigned int n) {
unsigned int value = n;
int i;
assert(n != 0);
for (i = 4; i >= 0; --i) {
const int shift = (1 << i);
const unsigned int x = value >> shift;
......
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