Examples. Ward 3. CS 160. Example 1: C to ARM Assembler. • C: x = (a + b) - c;. •
ARM: ADR r4,a .... Same C code; different ARM implementation. ARM:.
ARM Assembly Language Examples & Assembler ARM Assembly Language Examples
CS 160
Ward 1
Example 1: C to ARM Assembler • C:
Example 2: C to ARM Assembler y = a*(b+c);
• ARM:
• ARM:
CS 160
Ward 2
• C:
x = (a + b) - c; ADR LDR ADR LDR ADD ADR LDR SUB ADR STR
CS 160
r4,a r0,[r4] r4,b r1,[r4] r3,r0,r1 r4,c r2,[r4] r3,r3,r2 r4,x r3,[r4]
; ; ; ; ; ; ; ; ; ;
get address for a get value of a get address for b, reusing r4 get value of b compute a+b get address for c get value of c complete computation of x get address for x store value of x Ward 3
ADR LDR ADR LDR ADD ADR LDR MUL ADR STR CS 160
r4,b r0,[r4] r4,c r1,[r4] r2,r0,r1 r4,a r0,[r4] r2,r2,r0 r4,y r2,[r4]
; ; ; ; ; ; ; ; ; ;
get address for b get value of b get address for c get value of c compute partial result get address for a get value of a compute final value for y get address for y store y Ward 4
Example 3: C to ARM Assembler
Example 4: Condition Codes
• C:
C:
z = (a R0 and i = 0 ; is i < 15? ; j = j + j ; i++
Ward 7
; compute and test condition ADR r4,a ; get address for a LDR r0,[r4] ; get value of a ADR r4,b ; get address for b LDR r1,[r4] ; get value for b CMP r0,r1 ; compare a < b BGE fblock ; if a >= b, branch to false block
CS 160
Ward 8
Example 6: if statement [2] ; true block MOV r0,#5 ADR r4,x STR r0,[r4] ADR r4,c LDR r0,[r4] ADR r4,d LDR r1,[r4] ADD r0,r0,r1 ADR r4,y STR r0,[r4] B after
; ; ; ; ; ; ; ; ; ; ;
Example 6: if statement [3] ; false block fblock ADR r4,c LDR r0,[r4] ADR r4,d LDR r1,[r4] SUB r0,r0,r1 ADR r4,x STR r0,[r4] after ...
generate value for x get address for x store x get address for c get value of c get address for d get value of d compute y get address for y store y branch around false block
CS 160
Ward 9
Example 6: Heavy Conditional Instruction Use [1]
Same C code; different ARM implementation ARM:
ADR for LDR a ADR
CS 160
r4,a a r0,[r4] r4,b
; get address
; get address
Ward 10
Example 6: Heavy Conditional Instruction Use [2] r4,x r0,[r4] r4,c r0,[r4] r4,d r1,[r4] r0,r0,r1 r4,y r0,[r4]
; false block ADRGE r4,c
; get value of
Ward 11
get address for c get value of c get address for d get value for d compute a-b get address for x store value of x
CS 160
ADRLT STRLT ADRLT LDRLT ADRLT LDRLT ADDLT ADRLT STRLT
; Compute and test the condition
; ; ; ; ; ; ;
CS 160
; ; ; ; ; ; ; ; ;
get address for store x get address for get value of c get address for get value of d compute y get address for store y
x c d
y
; get address for c Ward 12
Example 6: Heavy Conditional Instruction Use [3] LDRGE ADRGE LDRGE SUBGE ADRGE STRGE
r0,[r4] r4,d r1,[r4] r0,r0,r1 r4,x r0,[r4]
; ; ; ; ; ;
get value of c get address for d get value for d compute a-b get address for x store value of x
CS 160
ARM Assembler
Ward 13
CS 160
Assembly Language Basics
CS 160
Ward 14
General Layout
Ward 15
CS 160
Ward 16
Simple Example Description
Assembly Directives
and memory type.
CS 160
Ward 17
CS 160
sum1.s: Compute 1+2+…+n AREA EXPORT ; r0 = ; r0 =
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sum2.s: Compute 1+2+…+n
SUM, CODE, READONLY sum1 input variable n output variable sum
AREA EXPORT ; r0 = ; r0 =
SUM, CODE, READONLY sum input variable n output variable sum
sum1 MOV
r1,#0
; set sum = 0
sum MLA MOV
sum_loop ADD SUBS BNE
r1,r1,r0 r0,r0,#1 sum_loop
; set sum = sum+n ; set n = n-1
sum_rtn MOV MOV
r0,r1 pc,lr
; set return value
sum_rtn MOV
r1,r0,r0,r0 r0,r1,LSR#1
; n*(n+1) = n*n + n ; divide by 2
pc,lr
END
END CS 160
Ward 19
CS 160
Ward 20
log.s: Compute k (n 1 continue if n != 0
log_rtn
CS 160
END
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