dll

;A 64-bit function that posterize values in 2^8 valuse
;
; The function has prototype:
;   void posterize(unsigned short[] array, uint64_t length, char levelNo)
; -----------------------------------------------------------------------------

; Gnu/Linux
; rdi – 1 argument - array
; rsi – 2 argument - length
; rdx – 3 argument - levelNo

; Windows (?)
; rcx - 1 argument
; rdx - 2 argument
; r8  - 3 argument

; r8b - vector capacity counter
; r9b - progVal
; r10b - half progVal
; r12  - table offset

    global  posterize
    section .text


calculate_progVal:
    ;calculate progging value step
    mv      rax, rdx
    div     maxByteVal
    mv      r9b, rax
    mv      r10b, r9b
    dec     r9b
    shrw    $1, %r10b

setUpStartValues:
    mov     r11b, 0;
    mov     r12,  0;
    mov     r8b, wordCounter;


posterize:
    cmp     rsi, 0  ; check if lenght <= 0
    jle     done


fill_vector:
    VMOVDQU16   zmm0, zmmword ptr [rdi+r12w]     ;fill vector
    sub     rsi, wordCounter    ;decrese vector lenght


transform:
    ; vaddsw -- add halfProgVal to vector
    mv      zmm1, zmm0
    ; vandpw -- modulo with progVal - 1
    vpsubw  zzm2, zmm1, zmm0 ;substract zzm0 zzm1, save in zzm2


save_values:
    vmovdqu16   zmmword ptr [rdi+r12],zmm2 ;save values to array
    add         r12, wordCounter
    jmp         posterize;


done:
    ret



    section .data
wordCounter:    db  32
maxByteVal:     db  255