kvisc/ka/str/strrev.k

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

;
; void strrev(char *buf, const char *str)
;
; buf and src must NOT overlap
;
strrev:
    test b[ax1], b[ax1]
    mov.z b[ax0], 0
    ret.z

    ; save str's location
    mov rdx, ax1

    ; go to str's end, just before
    ; the null terminator
.1:
    test b[ax1+1], b[ax1+1]
    inc.nz ax1
    jmp.nz .1

.2:
    ; copy, going backward though str
    ; and forward through buf
    mov b[ax0], b[ax1]

    cmp ax1, rdx
    mov.z b[ax0+1], 0
    ret.z

    inc ax0
    dec ax1
    jmp .2


;
; void strrev2(char *str)
;
; Inverses str
;
strrev2:
    test b[ax0], b[ax0]
    ret.z

    mov ax1, ax0

    ; go to str's end, just before
    ; the null terminator
.1:
    test b[ax1+1], b[ax1+1]
    inc.nz ax1
    jmp.nz .1

    ; increase ax0 while decreasing ax1, performing exchanges
.2:
    cmp ax0, ax1
    jmp.ae .3

    xchg b[ax0], b[ax1]

    inc ax0
    dec ax1
    jmp .2

.3:
    ret