1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
#include <stdio.h>
// x in rdi
// fun_b:
// movl $64, %edx i <- 64 (32 bits?, long presumably)
// movl $0, %eax val <- 0
// .L10:
// movq %rdi, %rcx tmp <- x
// andl $1, %ecx tmp <- tmp & 1
// addq %rax, %rax val <- val + val
// orq %rcx, %rax val <- val | tmp
// shrq %rdi
// subq $1, %rdx i <- i-1
// jne .L10 if i != 0 then goto .L10
// rep; ret
long fun_b(unsigned long x) {
long val = 0;
long i;
for (i = 64; i!=0; i--) {
long tmp = x;
tmp &= 1; // check 1 bit
val += val; // multiply by two
val |= tmp; // add 1 bit if present
x >>= 1; // shift next bit into 1 bit
}
return val;
}
// Seems to compute the value shifted to the left (63 - nbit), (or in other words the mirror image)
int main() {
printf("val: %ld, computed: %ld, bits: %lb\n", fun_b(10), (long) 10 << 59, 10);
return 0;
}
|
