; The OS/K Team licenses this file to you under the MIT license.
; See the LICENSE file in the project root for more information.

;
; int strnlen(char *, int)
;
strnlen:
    mov rcx, ax1
    scasb ax0, zero

    sub rax, ax1, rcx
    ret

;
; int strlen(char *)
;
strlen:
    mov rcx, STRLEN_MAX
    mov rdx, rcx
    scasb ax0, zero

    sub rax, rdx, rcx
    ret

;
; void strcpy(char *, const char *)
;
strcpy:
.l:
    mov rcx, b[ax1]
    mov b[ax0], rcx

    jrcxz .r

    inc ax0
    inc ax1

    jmp .l

.r:
    ret

;
; void strncpy(char *, const char *, int)
;
strncpy:
    mov rcx, ax2
    jrcxz .r

.l:
    mov b[ax0], b[ax1]

    inc ax0
    inc ax1

    loop .l

.r:
    ret

;
; void strnzcpy(char *, const char *, int)
;
strnzcpy:
    mov rcx, ax2
    jrcxz .r

.l:
    mov rax, b[ax1]
    mov b[ax0], rax

    jraxz .r

    inc ax0
    inc ax1

    loop .l

.z:
    nul b[ax0]

.r:
    ret

;
; int strcmp(const char *str1, const char *str2)
;
; Returns:
;    0 if the contents of both strings are equal
;   >0 if the first character that does not match has a greater value in str1 than in str2
;   <0 if the first character that does not match has a lower value in str1 than in str2
;
strcmp:
    nul rsi
.l:
    movzx rax, b[ax0+rsi]
    movzx rdx, b[ax1+rsi]

    bne rax, rdx, .r

    ; both zero?
    add rcx, rax, rdx
    jrcxz .r

    inc rsi
    jmp .l

.r:
    sub rax, rdx
    ret

;
; int strncmp(const char *str1, const char *str2, int maxn)
;
strncmp:
    mov rcx, ax2
    jrcxz .r

.l:
    movzx rax, b[ax0]
    movzx rdx, b[ax1]

    bne rax, rdx, .r

    inc ax0
    inc ax1
    loop .l

.r:
    sub rax, rdx
    ret

;
; char *strchrnul(const char *str, int ch)
;
strchrnul:
    mov rcx, STRLEN_MAX
    scasb ax0, ax1

    mov rax, ax0
    ret

;
; char *strchr(const char *str, int ch)
;
strchr:
    mov rcx, STRLEN_MAX
    scasb ax0, ax1

    bnz b[ax0], .r
    nul rax
    ret

.r:
    mov rax, ax0
    ret

;
; void strrev(char *buf, const char *str)
;
; buf and src must NOT overlap
;
strrev:
    bzr b[ax1], .z

    ; save str's location
    mov rsi, ax1

    ; go to str's end, just before
    ; the null terminator
    mov rcx, STRLEN_MAX
    scasb ax1, zero
    dec ax1

.l:
    ; copy, going backward though str
    ; and forward through buf
    mov b[ax0], b[ax1]

    beq ax1, rsi, .r

    inc ax0
    dec ax1
    jmp .l

.r:
    nul b[ax0+1]
    ret

.z:
    nul b[ax0]
    ret

;
; void strrev2(char *str)
;
; Inverses str
;
strrev2:
    bzr b[ax0], .r

    mov ax1, ax0

    ; go to str's end, just before
    ; the null terminator
    mov rcx, STRLEN_MAX
    scasb ax1, zero
    dec ax1

    ; increase ax0 while decreasing ax1, performing exchanges
.l:
    blteu ax1, ax0, .r

    xchg b[ax0], b[ax1]

    inc ax0
    dec ax1
    jmp .l

.r:
    ret