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/**
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0.
*/
/**
* FUNCTION: memset
*
* Override the version of memset used by CBMC.
* This takes advantage of the fact that 64bit operations require fewer array updates,
* which can make this version faster than the naive unrolling when used in CBMC.
* Benchmark your particular proof to know for sure.
*/
#include <stddef.h>
#include <stdint.h>
void *memset_using_uint64_impl(void *dst, int c, size_t n) {
__CPROVER_precondition(__CPROVER_w_ok(dst, n), "memset destination region writeable");
size_t num_uint64s = n >> 3;
size_t rem = n & 0x7;
uint8_t *d = (uint8_t *)dst;
// Use fallthrough to unroll the remainder loop
switch (rem) {
case 7:
d[6] = c;
case 6:
d[5] = c;
case 5:
d[4] = c;
case 4:
d[3] = c;
case 3:
d[2] = c;
case 2:
d[1] = c;
case 1:
d[0] = c;
}
d += rem;
uint64_t compounded = 0;
if (num_uint64s > 0 && c != 0) {
uint8_t *chars = (uint8_t *)&compounded;
chars[0] = c;
chars[1] = c;
chars[2] = c;
chars[3] = c;
chars[4] = c;
chars[5] = c;
chars[6] = c;
chars[7] = c;
}
for (size_t i = 0; i < num_uint64s; ++i) {
((uint64_t *)d)[i] = compounded;
}
return dst;
}
void *memset(void *s, int c, size_t n) {
return memset_using_uint64_impl(s, c, n);
}
void *__builtin___memset_chk(void *s, int c, size_t n, size_t os) {
(void)os;
return memset_using_uint64_impl(s, c, n);
}
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