Full time:
- 🏫 SWE at McMaster University
Free time:
- 👨💻 Von Neumann Enjoyer
- 🐧 FOSS Enthusiast
Interesting snippets
Stack UB (-O0)
void A() { int x = 42; }
int B() { int x; return x; }
int main() {
A();
printf("%d\n", B());
}Register UB (-O0)
void A(int x) {}
int B() { int x; return x; }
int main() {
A(42);
printf("%d\n", B());
}Computed GOTO
void jump(void* p) { goto* p; }
int main() {
void* p = &&foo;
jump(p);
printf("A\n");
foo:
printf("B\n");
}Faster switch
#include <cstdio>
#include <cstdint>
enum Instruction : uint8_t { Done, A, B, C };
void execute(const Instruction* list) {
constexpr void* labels[] = {
[Instruction::Done] = &&Done,
[Instruction::A] = &&A,
[Instruction::B] = &&B,
[Instruction::C] = &&C,
};
const auto next = [&] { return labels[*list++]; };
goto* next();
Done: return;
A: printf("A\n"); goto* next();
B: printf("B\n"); goto* next();
C: printf("C\n"); goto* next();
}
int main() {
constexpr Instruction list[] = {C, B, A, Done};
execute(list);
}Duff's device
#include <stddef.h>
#include <stdio.h>
void better_memcpy(void* restrict dest, void* restrict src, size_t n) {
unsigned char* to = dest;
unsigned char* from = src;
int remain = (n + 7) / 8;
switch (n % 8) {
case 0: do { *to++ = *from++;
case 7: *to++ = *from++;
case 6: *to++ = *from++;
case 5: *to++ = *from++;
case 4: *to++ = *from++;
case 3: *to++ = *from++;
case 2: *to++ = *from++;
case 1: *to++ = *from++;
} while (--remain > 0);
}
}
int main() {
int a[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };
int b[sizeof(a) / sizeof(a[0])];
better_memcpy(b, a, sizeof(b));
printf("%d\n", b[8]);
}Hello, World!
#define print(...) puts(#__VA_ARGS__)
int main() { print(Hello, World!); }int main() {
__uint128_t x = ((__uint128_t)0x290E4D9CB7 << 64) | 0xD740B37ECD996400;
while (x >>= 7) putchar(x & 0x7F);
}