diff options
Diffstat (limited to '3/10_control_and_data/49_variable_stack.c')
| -rw-r--r-- | 3/10_control_and_data/49_variable_stack.c | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/3/10_control_and_data/49_variable_stack.c b/3/10_control_and_data/49_variable_stack.c new file mode 100644 index 0000000..d72c235 --- /dev/null +++ b/3/10_control_and_data/49_variable_stack.c @@ -0,0 +1,81 @@ +// A. +// vframe: +// pushq %rbp +// movq %rsp, %rbp +// subq $16, %rsp +// leaq 22(,%rdi,8), %rax +// andq $-16, %rax +// +// +// bitlevel representation of -16 +// 1111111111111111111111111111111111111111111111111111111111110000 +// +// rax +// 22 + n*8 +// n=0 0000000000000000000000000000000000000000000000000000000000010110 22 +// n=1 0000000000000000000000000000000000000000000000000000000000011110 30 +// n=2 0000000000000000000000000000000000000000000000000000000000100110 38 +// n=3 0000000000000000000000000000000000000000000000000000000000101110 46 +// n=4 0000000000000000000000000000000000000000000000000000000000110110 54 +// n=5 0000000000000000000000000000000000000000000000000000000000111110 62 +// +// (22 + n*8) & -16 +// n=0 0000000000000000000000000000000000000000000000000000000000010000 16 8n+16 +// n=1 0000000000000000000000000000000000000000000000000000000000010000 16 8n+8 +// n=2 0000000000000000000000000000000000000000000000000000000000100000 32 8n+16 +// n=3 0000000000000000000000000000000000000000000000000000000000100000 32 8n+8 +// n=4 0000000000000000000000000000000000000000000000000000000000110000 48 +// n=5 0000000000000000000000000000000000000000000000000000000000110000 48 +// +// print("{:064b}".format((0*8+22) & -16)) +// print("{:064b}".format((1*8+22) & -16)) +// print("{:064b}".format((2*8+22) & -16)) +// print("{:064b}".format((3*8+22) & -16)) +// print("{:064b}".format((4*8+22) & -16)) +// print("{:064b}".format((5*8+22) & -16)) +// +// B. +// vframe: +// pushq %rbp +// movq %rsp, %rbp +// subq $16, %rsp +// leaq 22(,%rdi,8), %rax +// andq $-16, %rax +// +// subq %rax, %rsp +// +// leaq 7(%rsp), %rax rax <- (rsp+7) = (rsp+(n-1)), n = 8 +// shrq $3, %rax rax <- (floor(rax/8)) +// leaq 0(,%rax,8), %r8 r8 <- ceil(rsp/8)*8 +// +// Important We are growing the stack downwards. +// But the array index grows upwards. +// +// See 2.3.7 for derivation. +// If x%(1<<k) == 0 then the bias has no effect, rounding down does not happen, there is no fraction. +// else +// Since the operation of adding the bias and then flooring happens, +// this results in rounding towards zero, or taking the ceiling. +// +// So if rsp was a multiple of 8 then nothing happens. +// Otherwise the start of the array is set to the first multiple of 8 towards the bottom of the stack (ceil goes towards greater addresses of the bottom). +// +// C. +// +// s_2 = (- s_1 +// (+ (if (odd? n) 8 16) (* n 8) ) +// ) +// +// p = ceil(s2/8)*8 +// e2 = (- p s2) +// e1 = (- s2 s1 e2 8n) +// +// 2065 - (8+5*8) +// +// n s_1 s_2 p e_1 e_2 +// 5 2065 2017 2024 1 7 +// 6 2064 2000 2000 16 0 +// +// D. +// p is 8byte aligned owing to the 8-10 instructions. +// s2 is not guaranteed to be aligned, so 1 byte. (But all we are doing is subtracting multiples of 16 from s1... not sure how this helps) |