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creating random integers from seed value

M B

Hi, I'm trying to translate this code:
randomInteger =(((randomInteger * 214013) + 2531011) >> 16) & 0x7FFF ;

into assembly in order to create a random integer generator, I'm guessing I'm needing the LSR, AND or MOV instructions, but I'm not sure.

I'm in an introduction to ARM Assembly Language course, I'd appreciate any help

  • 0 in reply to Westonsupermare Pier

    again, there is no such thing as random generator code, only pseudorandom.

    a good way to get a truly random value is to have a free running timer and reading it on some external event

    Erik

  • 0 in reply to M B

    Well you could build a list of expected values with a C application on the PC.

    For the range you need to perform a %= 215 operation on the values.

  • 0 in reply to Westonsupermare Pier

    Hi, thanks so much for the response, here's what I've come up with:

    SRAM_BASE       EQU     0x40000000              ;static RAM location
                        AREA    StrCopy,CODE,READONLY
                        ENTRY

                        LDR             r1,=randomInteger       ;source
                        LDR             r0,=SRAM_BASE           ;destination
                        MOV             r3,#20                          ;counter
                        LDR             r4,=214013
                        LDR             r5,=2531011

random
                        CMP     r3,#0                           ;check for zero terminator
                        BLE     out1                            ;branch if no more out of loop
                        LDRH    r2,[r1],#2                      ;load word from source, update address
                        MUL     r6,r2,r1
                        MOV     r2,r6
                        ADDS    r2,r5
                        LSRS    r2,#16
                        LDR     r5,=0x7FFF
                        ANDS    r2,r5
                        STRH    r2,[r0],#2                      ;write halfword to destination, update address
                        SUB     r3,r3,#1                        ;decrement counter
                        B       random
out1
stop            B               stop
randomInteger           DCW     0x1234          ;seed value


                        END


    though I'm looking at the memory and I'm not certain I'm getting what I'm supposed to be getting. The basic objective is to write an ARM assembly program that will generate 20 pseudo-random integers in the range 0 to 215-1 and store the numbers in 20 consecutive halfword locations beginning at address 0x40000000.

  • 0 

    ; randomInteger =(((randomInteger * 214013) + 2531011) >> 16) & 0x7FFF ;

        ldr     r1, =214013
        ldr     r2, =2531011
        ldr     r3, =randomInteger
        ldr     r0, [r3]        ; load from randomInteger
        mul     r0, r1          ; *= 214013
        adds    r0, r2          ; += 2531011
        lsrs    r0, #16         ; >>= 16
        ldr     r2, =0x7FFF
        ands    r0, r2          ; &= 0x7FFF
        str     r0, [r3]        ; store to randomInteger
; ...

; data section
randomInteger dcd 0x1234