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kvisc/ka/crt/str/strrev.k

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; 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)
;
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; buf and src must NOT overlap
;
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strrev:
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cmp b[ax1], 0
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mov.z b[ax0], 0
ret.z
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; save str's location
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mov lx0, ax1
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; go to str's end, just before
; the null terminator
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mov rcx, STRLEN_MAX
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scasb.rep.nz ax1, 0
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dec ax1
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.2:
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; copy, going backward though str
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; and forward through buf
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mov b[ax0], b[ax1]
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cmp ax1, lx0
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mov.z b[ax0+1], 0
ret.z
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inc ax0
dec ax1
jmp .2
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;
; void strrev2(char *str)
;
; Inverses str
;
strrev2:
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cmp b[ax0], 0
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ret.z
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mov ax1, ax0
; go to str's end, just before
; the null terminator
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mov rcx, STRLEN_MAX
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scasb.rep.nz ax1, 0
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dec ax1
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; increase ax0 while decreasing ax1, performing exchanges
.2:
cmp ax0, ax1
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j.ae .3
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xchg b[ax0], b[ax1]
inc ax0
dec ax1
jmp .2
.3:
ret