decompressor: Add memory routines

decompressor/mem.asm

@@ -0,0 +1,75 @@
+section .text
+
+global memcpy
+memcpy:
+    push esi
+    push edi
+    mov eax, dword [esp+12]
+    mov edi, eax
+    mov esi, dword [esp+16]
+    mov ecx, dword [esp+20]
+    rep movsb
+    pop edi
+    pop esi
+    ret
+
+global memset
+memset:
+    push edi
+    mov edx, dword [esp+8]
+    mov edi, edx
+    mov eax, dword [esp+12]
+    mov ecx, dword [esp+16]
+    rep stosb
+    mov eax, edx
+    pop edi
+    ret
+
+global memmove
+memmove:
+    push esi
+    push edi
+    mov eax, dword [esp+12]
+    mov edi, eax
+    mov esi, dword [esp+16]
+    mov ecx, dword [esp+20]
+
+    cmp edi, esi
+    ja .copy_backwards
+
+    rep movsb
+    jmp .done
+
+  .copy_backwards:
+    lea edi, [edi+ecx-1]
+    lea esi, [esi+ecx-1]
+    std
+    rep movsb
+    cld
+
+  .done:
+    pop edi
+    pop esi
+    ret
+
+global memcmp
+memcmp:
+    push esi
+    push edi
+    mov edi, dword [esp+12]
+    mov esi, dword [esp+16]
+    mov ecx, dword [esp+20]
+    repe cmpsb
+    jecxz .equal
+    mov al, byte [edi-1]
+    sub al, byte [esi-1]
+    movsx eax, al
+    jmp .done
+
+  .equal:
+    xor eax, eax
+
+  .done:
+    pop edi
+    pop esi
+    ret