INSTRUCTION SET
S3C4510B
Division and Remainder
A number of divide routines for specific applications are provided in source form as part of the ANSI C library
provided with the ARM Cross development toolkit, available from your supplier. A short general purpose divide
routine follows.
; Enter with numbers in Ra and Rb.
MOV
Rcnt,#1
; Bit to control the division.
Div1
Div2
CMP
Rb,#0x80000000
Rb,Ra
Rb,Rb,ASL#1
Rcnt,Rcnt,ASL#1
Div1
; Move Rb until greater than Ra.
CMPCC
MOVCC
MOVCC
BCC
MOV
CMP
SUBCS
ADDCS
MOVS
MOVNE
BNE
Rc,#0
Ra,Rb
; Test for possible subtraction.
; Subtract if ok,
; Put relevant bit into result
; Shift control bit
; Halve unless finished.
; Divide result in Rc, remainder in Ra.
Ra,Ra,Rb
Rc,Rc,Rcnt
Rcnt,Rcnt,LSR#1
Rb,Rb,LSR#1
Div2
Overflow Detection in the ARM7TDMI
1. Overflow in unsigned multiply with a 32-bit result
UMULL
TEQ
Rd,Rt,Rm,Rn
Rt,#0
; 3 to 6 cycles
; +1 cycle and a register
BNE
overflow
2. Overflow in signed multiply with a 32-bit result
SMULL
TEQ
BNE
Rd,Rt,Rm,Rn
Rt,Rd ASR#31
overflow
; 3 to 6 cycles
; +1 cycle and a register
3. Overflow in unsigned multiply accumulate with a 32 bit result
UMLAL
TEQ
Rd,Rt,Rm,Rn
Rt,#0
; 4 to 7 cycles
; +1 cycle and a register
BNE
overflow
4. Overflow in signed multiply accumulate with a 32 bit result
SMLAL
TEQ
BNE
Rd,Rt,Rm,Rn
Rt,Rd, ASR#31
overflow
; 4 to 7 cycles
; +1 cycle and a register
3-60
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