;x86-64 assembly code for Microsoft Windows
;Tested in windows 7 Enterprise Service Pack 1 64 bit
;With the AMD FX(tm)-6300 processor
;Assembled with NASM version 2.11.06
;Linked to C library with gcc version 4.9.2 (x86_64-win32-seh-rev1, Built by MinGW-W64 project)

;Assembled and linked with the following commands:
;nasm -f win64 <filename>.asm -o <filename>.obj
;gcc <filename>.obj -o <filename>

;Takes number of iterations to run RNG loop as command line parameter.

extern printf,puts,atoi,exit,time,_aligned_malloc

section .data
align 64
errmsg_argnumber: db "There should be no more than one argument.",0
align 64
errmsg_noarg: db "Number of iterations was not specified.",0
align 64
errmsg_zeroiterations: db "Zero iterations of RNG loop specified.",0

align 64
errmsg_timefail: db "Unable to retrieve calender time.",0
align 64
errmsg_mallocfail: db "Unable to allocate memory for array of random numbers.",0

align 64
fmt_random: db "The %u number generated is %d",0xa,0xd,0

align 16
multiplier: dd 214013,17405,214013,69069
align 16
addend: dd 2531011, 10395331, 13737667, 1
align 16
mask: dd  0xffffffff,0,0xffffffff,0
align 16
masklo: dd 0x7fff,0x7fff,0x7fff,0x7fff

section .bss

section .text
global main

main:

;check for argument
cmp rcx,1
jle err_noarg

;ensure that only one argument was entered
cmp rcx,2
jg err_argnumber


;get number of times to iterate get_random
mov rcx,[rdx + 8]
call atoi


;ensure that number of iterations is greater than 0
cmp rax,0
jle err_zeroiterations
mov rcx,rax


;calculate space needed for an array containing the random numbers
shl rcx,4

;move size of array into r14
mov r14,rcx

;16 byte alignment boundary
mov rdx,16

;reserve memory aligned to 16 byte boundary for array with _aligned_malloc
call _aligned_malloc

cmp rax,0
jz err_mallocfail

;pointer to array in r15
mov r15,rax


;seed the RNG using time()
xor rcx,rcx
call time

;ensure that time returns valid output
cmp rax,-1
jz err_timefail


;pointer to array of random numbers in r15
;address of end of array at in r14
;states stored in xmm0

;calculate address of end of array in r14
add r14,r15

;load seed,seed+1,seed,seed+1 into xmm0
lea rbx,[rax - 1]
shl rax,32
or rax,rbx

movq xmm0,rax
vpslldq xmm1,xmm0,8
vpor xmm0,xmm0,xmm1


;pointer to array of random numbers in r15
;address of end of array in r14
;current address in array in rdi
;current states in xmm0
;multiplier in xmm1
;addened in xmm2
;mask in xmm3
;masklo in xmm4
;split seed in xmm5
;current set of random numbers in xmm6

;prepare random number generator

mov rdi,r15

vmovdqa xmm1,[multiplier]
vmovdqa xmm2,[addend]
vmovdqa xmm3,[mask]
vmovdqa xmm4,[masklo]


get_random:

;arrange order of current states to 2,3,0,1 and store in split seed
vpshufd xmm5,xmm0,10110001b

;multiply current states by multiplier
vpmulld xmm0,xmm0,xmm1

;set order of multiplier to 2,3,0,1
vpshufd xmm1,xmm1,10110001b

;multiply split seed by multiplier
vpmulld xmm5,xmm5,xmm1

;and current states with mask
vpand xmm0,xmm0,xmm3

;and current split seed with mask
vpand xmm5,xmm5,xmm3

;set order of split seed to 2,3,0,1
vpshufd xmm5,xmm5,10110001b

;or current states with split seed
vpor xmm0,xmm0,xmm5

;add adder to current states
vpaddd xmm0,xmm0,xmm2


;shift vector right by two bytes
vpsrldq xmm6,xmm0,2

;and each state with 0x7fff
vpand xmm6,xmm6,xmm4

vmovdqa [rdi],xmm6

add rdi,16
cmp rdi,r14
jl get_random


;pointer to array of random numbers in r15
;address of end of array in r14
;current address in array in rdi
;array index in rsi


xor rsi,rsi
mov rdi,r15

print_random:

mov rcx,fmt_random
mov rdx,rsi
mov r8d,[rdi]
call printf

add rsi,1
add rdi,4
cmp rdi,r14
jl print_random

xor rcx,rcx
call exit


;;;;;;;;;;ERROR MESSAGES;;;;;;;;;;;;;;;;

err_argnumber:

mov rcx,errmsg_argnumber
call puts

jmp exit_one


err_noarg:

mov rcx,errmsg_noarg
call puts

jmp exit_one


err_zeroiterations:

mov rcx,errmsg_zeroiterations
call puts

jmp exit_one


err_timefail:

mov rcx,errmsg_timefail
call puts

jmp exit_one


err_mallocfail:

mov rcx,errmsg_mallocfail
call puts


exit_one:

mov rcx,1
call exit