ARM 教材 - cortex-m - 5 - 算數 - Arithmetic

Index: Data Processing


Hackpad

加減(反向減)乘除 

算數運算 : ADD / ADC / SUB / SBC /  RSB 

•        multiply and divide

•        

加: ADD

e.g. ADD R2, R1, R0  ; R2=R1+R0

e.g. ADD R2, R0, #2 ; R2=R1+2

e.g. ADD R2, R0 ; R2 += R0
e.g. ADD R8, R7, #&FF  ;  r8  = r7 & 0x000000FF

ADC: Add with carry

e.g. ADC R2, R1, R0   ; R2 = R1 + R0 + C

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減: SUB

e.g. SUB R0, R1, #6 ; R0=R1-6

e.g. RSB R0, R1, #6 ; R0=6-R1

SBC : sub with carry
e.g. SBC  R0, R1, R2   ; R0 = R1- R2 +C -1

RSB: reverse subtraction
RSC: reverse subtraction with carry

• RSB    r0, r1, r2    ; r0 := r2 - r1

• RSC    r0, r1, r2    ; r0 := r2 - r1 + C - 1

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乘: MUL

R4 = 0x00000077 (119)

R3 = 0xFFFFFF10 (-240)

MUL R5, R4, R3

R5 = 0xFFFF9070 (-28560)

overflow: 

R6=0x0000BEAD (48813)

R7=0x000157B5 (87989)

MUL R8, R6, R7

R8 = 0x00009B51 (39761) => 4295007057 (0x100009B51)

MLS : multiply with subtract 

MLS R4,R5,R6,R7 ; R4 = R7-(R5*R6)

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除: UDIV (unsigned) SDIV (signed)

R2=0x4

R0=0x2

UDIV R3, R2, R0

R3=0x2

R1=0x3

R2=0x4

UDIV R4, R2, R1

R4=0x1

UDIV R5, R1, R2

R5=0x0

R6 = 0xFFFFFF00 (4294967040) (-256)

R7 = 0x5

UDIV R8, R6, R7

SDIV R9, R6, R7

R8 = 0x33333300 (858993408)

R9 = 0xFFFFFFCD (-51)

除法餘數 (%) 如何 implement

Ref: https://blog.feabhas.com/2010/10/embedded-programmers-guide-to-the-arm-cortex-m-architecture/

• r0 ; time ; 

• ARM function call 參數並不是都推到 stack. 前幾個會直接帶在 r0-r3 來加速  

calling convetion

• time % 60 => 搭配除法乘法得到餘數, 沒有單一指令

• r2 = time / 60;

• ret = time - (60*r2)

MLS r0, r1, r2, r0 ;  r0 = r0 - (r1*r2)

basic integer math operation 

Ref: https://embedded2016.hackpad.com/ARM-Architecture-z5hdXADIEm2