Get rid of ugly if statements

Question

I have this ugly code:

if ( v > 10 ) size = 6;
if ( v > 22 ) size = 5;
if ( v > 51 ) size = 4;
if ( v > 68 ) size = 3;
if ( v > 117 ) size = 2         


        

Answer 1

You could rewrite it in ARM code. It's only 7 cycles worst case and a slender 164 bytes. Hope that helps. (note: this is untested)

; On entry
;   r0 - undefined
;   r1 - value to test
;   lr - return address
; On exit
;   r0 - new value or preserved
;   r1 - corrupted
;
wtf
        SUBS    r1, r1, #10
        MOVLE   pc, lr
        CMP     r1, #135
        MOVGT   r0, #1
        ADRLE   r0, lut
        LDRLEB  r0, [r0, r1]
        MOV     pc, lr
;
; Look-up-table
lut
        DCB     0   ; padding
        DCB     6   ; r1 = 11 on entry
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     6
        DCB     5   ; r1 = 23 on entry
        DCB     5
        ...
        ALIGN