Write an ARM assembly language routine to count the number of 1s in a 32bit word in r0 and return the result in r1.
code:
The following image is a screendump after executing the above code. Register r3 contains 0x13 which is 19, the number of 1s in 0x11AB003F.
LDR r0, 0x11AB003F dummy value for rl (11 ones) MOV r1,#0x0 MOV r2,#32 MOVS r0,r0, ROR #1 ADDCS r1,r1,#1 SUBS r2 , r2 , #1 BNE OnesCount ; clear ones counter ;use r2 as the loop counter i Repeat: rotate ro right set Ilags ;if carry set increment 1s counter ; decrement loop counter until all bits tested OnesCount If this was a subroutine Count, the code might be area test, cODE, readwrite ADR sp, Stackl LDR r2 , =0xFFFFFFFF STR r2, [sp] LDR r0, - 0xFFAB123A BL MOV r3,rl NOP NOP ;set up dummy r2 ; dummy data :call routine ; read result Count STMFD sp!, (r2,lr] MOV r1, #0x0 MOV r2,#4 Count ; save r2 and return on the stack onesCount MOVS r0,r0, ROR #1 ADDCS r1,r1,#1 SUBS r2 , r2 , #1 BNE OnesCount LDMFD sp!, (r2,pc) ; restore r2 and returr Stack Stackl DCD 0,0,0,0,0 DCD 0,0,0,0,0 CAUsers AlanCore7 Desktop ForBrusselsMay2012\Chap3Problems.uvproj - pVision4 File Edit iew Project Flash Debug Peripherals Tools SVCS Window Help Registers 3Chap3Problems.asm area test, CoDE, readwrite ADR p, Stackl LDR r2,=0xEEEEEEEE STR r2, [ap] LDR ro, - 0XEEAB123A ;dummy data BL Count MOV 3,rl B Parkilere RegisterValue0 Current OF FAB123A 0x00000013 :set up dumay x2 R1 000000013 call routine : read result endless loop R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 (5P) 0x00000054 R14 (LR) 000000014 R15 (PC) 000000018 0 ParkHere NOP 0 count STMED sp!, 2,1x) MOV Nov saver and return on the stacik r1, #0x0 r2, #32 13 onescount Movs ro,r0 , ROR #1 ADDcs r1,r1, #1 SUBS r2, r2, 1 BNE Onescount 15 restore r2 and return Stack DCD o,o, o, 0,0 User/System Fast Interrupt Interrupt 20 Stack DCD 0,0,0,0,0 21 END Project E Registers Simulation LDR r0, 0x11AB003F dummy value for rl (11 ones) MOV r1,#0x0 MOV r2,#32 MOVS r0,r0, ROR #1 ADDCS r1,r1,#1 SUBS r2 , r2 , #1 BNE OnesCount ; clear ones counter ;use r2 as the loop counter i Repeat: rotate ro right set Ilags ;if carry set increment 1s counter ; decrement loop counter until all bits tested OnesCount If this was a subroutine Count, the code might be area test, cODE, readwrite ADR sp, Stackl LDR r2 , =0xFFFFFFFF STR r2, [sp] LDR r0, - 0xFFAB123A BL MOV r3,rl NOP NOP ;set up dummy r2 ; dummy data :call routine ; read result Count STMFD sp!, (r2,lr] MOV r1, #0x0 MOV r2,#4 Count ; save r2 and return on the stack onesCount MOVS r0,r0, ROR #1 ADDCS r1,r1,#1 SUBS r2 , r2 , #1 BNE OnesCount LDMFD sp!, (r2,pc) ; restore r2 and returr Stack Stackl DCD 0,0,0,0,0 DCD 0,0,0,0,0 CAUsers AlanCore7 Desktop ForBrusselsMay2012\Chap3Problems.uvproj - pVision4 File Edit iew Project Flash Debug Peripherals Tools SVCS Window Help Registers 3Chap3Problems.asm area test, CoDE, readwrite ADR p, Stackl LDR r2,=0xEEEEEEEE STR r2, [ap] LDR ro, - 0XEEAB123A ;dummy data BL Count MOV 3,rl B Parkilere RegisterValue0 Current OF FAB123A 0x00000013 :set up dumay x2 R1 000000013 call routine : read result endless loop R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 (5P) 0x00000054 R14 (LR) 000000014 R15 (PC) 000000018 0 ParkHere NOP 0 count STMED sp!, 2,1x) MOV Nov saver and return on the stacik r1, #0x0 r2, #32 13 onescount Movs ro,r0 , ROR #1 ADDcs r1,r1, #1 SUBS r2, r2, 1 BNE Onescount 15 restore r2 and return Stack DCD o,o, o, 0,0 User/System Fast Interrupt Interrupt 20 Stack DCD 0,0,0,0,0 21 END Project E Registers Simulation
