This demo compares two techniques, sequential comparison versus a table based branching. The table based system has a fixed number of instructions for small to very large ranges.
comment # «»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
Comparison of two techniques, sequential comparison versus a table based branching system
that can handle very large ranges without speed loss with its fixed instruction count
«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«» #
include \masm64\include64\masm64rt.inc
.code
; «»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
entry_point proc
rcall sequential_cmp,0
rcall sequential_cmp,1
rcall sequential_cmp,2
rcall table_branch,0
rcall table_branch,1
rcall table_branch,2
rcall table_branch,3
.exit
entry_point endp
; «»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
sequential_cmp proc num1:QWORD
cmp num1, 0
jne @F
rcall MessageBox,0,str$(num1),"sequential Zero",MB_OK
ret
@@:
cmp num1, 1
jne @F
rcall MessageBox,0,str$(num1),"sequential One",MB_OK
ret
@@:
cmp num1, 2
jne @F
rcall MessageBox,0,str$(num1),"sequential Two",MB_OK
ret
@@:
ret
sequential_cmp endp
; «»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
table_branch proc num1:QWORD ; input range, 0 to 2
.data
lbls dq lbl0,lbl1,lbl2 ; table of labels
.code
mov rax, num1 ; load input into rax
cmp rax,2 ; test for range
jna @F
rcall MessageBox,0,"Number out of range","Table Branch Error",MB_OK
ret
@@:
lea rdx, lbls ; load table offset
jmp QWORD PTR [rdx][rax*8] ; branch to offset + input * 8
lbl0:
rcall MessageBox,0,str$(num1),"table branch Zero",MB_OK
ret
lbl1:
rcall MessageBox,0,str$(num1),"table branch One",MB_OK
ret
lbl2:
rcall MessageBox,0,str$(num1),"table branch Two",MB_OK
ret
table_branch endp
; «»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
end
Timings?
David,
Don't let me stop you. I have it done, have used the technique for years and if you need very fast options by number, its genuinely fast but seriously I don't have time to write a benchmark.