Xoroshiro32PlusPlus

; input: pointer to 32-bit seed
; output: random value between [0, 65535]
Xoroshiro32PlusPlus:
        ldrh    r3, [r0]
        push    {r4, r5, lr}
        movs    r4, r3
        ldrh    r2, [r0, #2]
        lsls    r5, r3, #13
        lsrs    r1, r3, #3
        eors    r4, r2
        orrs    r1, r5
        eors    r1, r4
        lsls    r5, r4, #5
        eors    r1, r5
        strh    r1, [r0]
        lsrs    r1, r4, #6
        lsls    r4, r4, #10
        adds    r2, r3, r2
        orrs    r4, r1
        strh    r4, [r0, #2]
        lsls    r0, r2, #16
        lsrs    r0, r0, #23
        lsls    r2, r2, #9
        orrs    r0, r2
        subs    r3, r3, #1
        adds    r0, r0, r3
        lsls    r0, r0, #16
        lsrs    r0, r0, #16
        pop     {r4, r5, pc}

; Compiled from:
; #include <stdint.h>
;
; const uint16_t a = 13;
; const uint16_t b = 5;
; const uint16_t c = 10;
; const uint16_t d = 9;
;
; static inline uint16_t rol(uint16_t x, uint16_t k)
; {
;     return (x << k) | (x >> ((sizeof(x) * 8) - k));
; }
;
; uint16_t Xoroshiro32PlusPlus(uint16_t * seed) {
;     uint16_t result = rol(seed[0] + seed[1], d) + seed[0];
;
;     seed[1] ^= seed[0];
;     seed[0] = rol(seed[0], a) ^ seed[1] ^ (seed[1] << b);
;     seed[1] = rol(seed[1], c);
;
;
;     return result - 1;
; }