Annotated zslGetRank

gistfile1.asm

Dump of assembler code for function zslGetRank:

; Function prolog: save registers on the stack
   0x0000000000427fd0 <+0>:     push   %r14
   0x0000000000427fd2 <+2>:     push   %r13
   0x0000000000427fd4 <+4>:     mov    %rsi,%r13
   0x0000000000427fd7 <+7>:     push   %r12
   0x0000000000427fd9 <+9>:     push   %rbp
   0x0000000000427fda <+10>:    push   %rbx
   0x0000000000427fdb <+11>:    sub    $0x10,%rsp

; i = zsl->level-1 (r14) and x = zsl->header (rbx)
   0x0000000000427fdf <+15>:    mov    0x18(%rdi),%r14d
   0x0000000000427fe3 <+19>:    mov    (%rdi),%rbx
   0x0000000000427fe6 <+22>:    sub    $0x1,%r14d

; initial test of for loop
   0x0000000000427fea <+26>:    js     0x428076 <zslGetRank+166>
   0x0000000000427ff0 <+32>:    xor    %r12d,%r12d
   0x0000000000427ff3 <+35>:    nopl   0x0(%rax,%rax,1)

; rbp will contain the offset to point to x->level[i]
; optimization of the compiler here:
; 3*8+(i*16) = 8 + 2*8 + 16*i = 8 + 16*(i+1)
; rax = x->level[i].forward
   0x0000000000427ff8 <+40>:    movslq %r14d,%rbp
   0x0000000000427ffb <+43>:    add    $0x1,%rbp
   0x0000000000427fff <+47>:    shl    $0x4,%rbp
   0x0000000000428003 <+51>:    mov    0x8(%rbx,%rbp,1),%rax

; Check x->level[i].forward is not nul
   0x0000000000428008 <+56>:    test   %rax,%rax
   0x000000000042800b <+59>:    je     0x428052 <zslGetRank+130>
   0x000000000042800d <+61>:    nopl   (%rax)

; Check score 
   0x0000000000428010 <+64>:    movsd  0x8(%rax),%xmm1
   0x0000000000428015 <+69>:    ucomisd %xmm1,%xmm0
   0x0000000000428019 <+73>:    ja     0x42803c <zslGetRank+108>
   0x000000000042801b <+75>:    ucomisd %xmm0,%xmm1
   0x000000000042801f <+79>:    jne    0x428052 <zslGetRank+130>
   0x0000000000428021 <+81>:    jp     0x428052 <zslGetRank+130>

; rdi = x->level[i].forward->obj, calling compareStringObjects
   0x0000000000428023 <+83>:    mov    (%rax),%rdi
   0x0000000000428026 <+86>:    mov    %r13,%rsi
   0x0000000000428029 <+89>:    movsd  %xmm0,(%rsp)
   0x000000000042802e <+94>:    callq  0x41b840 <compareStringObjects>
   0x0000000000428033 <+99>:    test   %eax,%eax
   0x0000000000428035 <+101>:   movsd  (%rsp),%xmm0
   0x000000000042803a <+106>:   jg     0x428052 <zslGetRank+130>

; eax = x->level[i].span
   0x000000000042803c <+108>:   mov    0x10(%rbp,%rbx,1),%eax

; x = x->level[i].forward (still in rbx)
   0x0000000000428040 <+112>:   mov    0x8(%rbx,%rbp,1),%rbx

; accumulate rank, eax being the low part of rax
   0x0000000000428045 <+117>:   add    %rax,%r12

; again rax = x->level[i].forward, test, and loop
   0x0000000000428048 <+120>:   mov    0x8(%rbx,%rbp,1),%rax
   0x000000000042804d <+125>:   test   %rax,%rax
   0x0000000000428050 <+128>:   jne    0x428010 <zslGetRank+64>

; rbx still represents x, compare x->obj
   0x0000000000428052 <+130>:   mov    (%rbx),%rdi
   0x0000000000428055 <+133>:   test   %rdi,%rdi
   0x0000000000428058 <+136>:   je     0x428070 <zslGetRank+160>

; call equalStringObjects and compare results
   0x000000000042805a <+138>:   mov    %r13,%rsi
   0x000000000042805d <+141>:   movsd  %xmm0,(%rsp)
   0x0000000000428062 <+146>:   callq  0x41b910 <equalStringObjects>
   0x0000000000428067 <+151>:   test   %eax,%eax
   0x0000000000428069 <+153>:   movsd  (%rsp),%xmm0

; return rank if test is true
   0x000000000042806e <+158>:   jne    0x428079 <zslGetRank+169>

; end of for loop, i is decremented
   0x0000000000428070 <+160>:   sub    $0x1,%r14d
   0x0000000000428074 <+164>:   jns    0x427ff8 <zslGetRank+40>

; return 0, and function epilog
   0x0000000000428076 <+166>:   xor    %r12d,%r12d
   0x0000000000428079 <+169>:   add    $0x10,%rsp
   0x000000000042807d <+173>:   mov    %r12,%rax
   0x0000000000428080 <+176>:   pop    %rbx
   0x0000000000428081 <+177>:   pop    %rbp
   0x0000000000428082 <+178>:   pop    %r12
   0x0000000000428084 <+180>:   pop    %r13
   0x0000000000428086 <+182>:   pop    %r14
   0x0000000000428088 <+184>:   retq