Nightloader/i386/legacy-boot/src-asm/utility/memory.asm

mem_copy:
    ; todo(perf): Copy multiple bytes at once
.prolog:
    push esi
    sub esp, 64
    mov esi, esp

    ; Save registers
    mov [esi + (64 - 4)], eax
    mov [esi + (64 - 8)], ebx
    mov [esi + (64 - 12)], ecx
    mov [esi + (64 - 16)], edx
    mov [esi + (64 - 20)], edi

.body:
    mov edx, [ebp - 4]      ; Destination
    mov edi, [ebp - 8]      ; Source
    xor eax, eax            ; Current Byte Offset

.body.copy_loop:

    mov ebx, edi
    add ebx, eax
    mov cl, [ebx]

    mov ebx, edx
    add ebx, eax
    mov [ebx], cl

    inc eax
    cmp eax, [ebp - 12]
    jb .body.copy_loop

.epilog:

    ; Restore registers
    mov eax, [esi + (64 - 4)]
    mov ebx, [esi + (64 - 8)]
    mov ecx, [esi + (64 - 12)]
    mov edx, [esi + (64 - 16)]
    mov edi, [esi + (64 - 20)]

    add esp, 64
    pop esi
    ret



; Furthest from EBP
; 3. Length of block 1 and block 2
; 2. Block 2
; 1. Block 1
; Nearest to EBP
mem_equal:
.prolog:
    push esi
    sub esp, 32
    mov esi, esp

    ; Save registers
    mov [esi + (32 - 4)], ebx
    mov [esi + (32 - 8)], ecx
    mov [esi + (32 - 12)], edx
    mov [esi + (32 - 16)], edi

.body:
    xor eax, eax            ; Current Byte Offset

.comparison_loop:
    mov edx, [ebp - 4]      ; Block 1
    mov ebx, edx
    add ebx, eax
    mov dl, [ebx]

    mov edi, [ebp - 8]      ; Block 2
    mov ebx, edi
    add ebx, eax
    mov dh, [ebx]

    inc eax
    cmp dl, dh
    je .length_condition

    ; On NOT equal
    xor eax, eax
    jmp .epilog

.length_condition:
    inc eax
    cmp eax, [ebp - 12]
    jb .comparison_loop
    mov eax, 1

.epilog:
    ; Restore registers
    mov ebx, [esi + (32 - 4)]
    mov ecx, [esi + (32 - 8)]
    mov edx, [esi + (32 - 12)]
    mov edi, [esi + (32 - 16)]

    add esp, 32
    pop esi
    ret



; ebp - 4: Area Pointer
; ebp - 8: Length of Area
; ebp - 12: Byte Value to set
mem_set:
.prolog:
    push esi
    sub esp, 64
    mov esi, esp

    ; Save registers
    mov [esi + (64 - 4)], eax
    mov [esi + (64 - 8)], ebx
    mov [esi + (64 - 12)], ecx
    mov [esi + (64 - 16)], edx
    mov [esi + (64 - 20)], edi

.body:
    mov ebx, [ebp - 4]
    mov dl, [ebp - 12]
    ; Make EDI the Last Byte Pointer
    mov edi, [ebp - 4]
    add edi, [ebp - 8]

.body.setter_loop:
    cmp ebx, edi
    jae .epilog

    mov [ebx], dl

    inc ebx
    jb .body.setter_loop

.epilog:
    ; Restore registers
    mov eax, [esi + (64 - 4)]
    mov ebx, [esi + (64 - 8)]
    mov ecx, [esi + (64 - 12)]
    mov edx, [esi + (64 - 16)]
    mov edi, [esi + (64 - 20)]

    add esp, 64
    pop esi
    ret