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bytes.cpp
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bytes.cpp
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#include <stdio.h>
#include <assert.h>
#include <string>
// Print the values at *ptr byte by byte
template <class T>
void write_bytes_seq(const T *ptr) {
uint8_t *ptr_i = (uint8_t*)ptr;
printf("%lu:", sizeof(T));
// print each byte
for(int i=0; i < sizeof(T); i++) {
// print the first 4 bits
printf("%x", ptr_i[i] >> 4);
// print the second 4 bits
printf("%x", ptr_i[i] & 0xf);
}
}
template <class T>
void pptr_seq(const char *lbl, T *ptr) {
// print label
printf("S %s: ", lbl);
// print hex value
write_bytes_seq(ptr);
printf(" | 0x%016llx", (u_int64_t)ptr);
printf("\n");
}
// Print the value at *ptr
template <class T>
void write_bytes(const T *ptr) {
char fmt[8] = "%";
sprintf(fmt+strlen(fmt), "0%lux", 2 * sizeof(T));
printf("%lu:", sizeof(T));
printf(fmt, *ptr);
}
template <class T>
void pptr(const char *lbl, T *ptr) {
// print label
printf("N %s: ", lbl);
// print hex value
write_bytes(ptr);
printf(" | 0x%016llx", (u_int64_t)ptr);
printf("\n");
}
#define WTYPE uint32_t
#define SHIFT 1
int main(int argc, char **argv) {
// allocate 8 bytes on the stack
uint64_t buf = 0;
// make a 4 byte int pointer to the 0-3rd bytes of buf
WTYPE *good = (WTYPE*)&buf;
pptr_seq("init", good);
pptr("init", good);
printf("\n");
// make sure *good is aligned on a 4 byte boundary
assert(0 == (uint64_t)good % sizeof(uint32_t));
// write a value to 'good' and read it back
*good = 0x12345678;
pptr_seq("good", good);
pptr("good", good);
printf("\n");
// make a 4 byte int pointer to the first 1-4th (misaligned)
WTYPE *bad = (WTYPE*)((uint64_t)good + SHIFT);
// make sure *bad is misaligned by 1 byte
assert(SHIFT == (uint64_t)bad % sizeof(uint32_t));
// write a value to 'bad' and read it back
*bad = 0x90abcdef;
pptr_seq("bad", bad);
pptr("bad", bad);
printf("\n");
pptr_seq("good2", good);
pptr("good2", good);
printf("\n");
}