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/* ------------------------------------------------------------------ */
/* | Copyright Unpublished, MIPS Computer Systems, Inc. All Rights | */
/* | Reserved. This software contains proprietary and confidential | */
/* | information of MIPS and its suppliers. Use, disclosure or | */
/* | reproduction is prohibited without the prior express written | */
/* | consent of MIPS. | */
/* ------------------------------------------------------------------ */
/* strcat.s 1.1 */
/* This function is an assembly-code replacement for the libc function
* strcat.
* strcat and strcpy are very similar, but we waste about 40 words of
* code when both are used, so that they can be independently replaced.
* There are one caveat to consider: this function is written in
* assembler code, and as such, cannot be merged using the U-code
* loader. */
/* Craig Hansen - 3-September-86 */
#include <kxmips.h>
/* It turns out better to think of lwl/lwr and swl/swr as
smaller-vs-bigger address rather than left-vs-right.
Such a representation makes the code endian-independent. */
#define LWS lwr
#define LWB lwl
#define SWS swr
#define SWB swl
.text
LEAF_ENTRY(strcat)
.set noreorder
// a0/ destination
// a1/ source
move v0, a0 # a copy of destination address is returned
$findz: lb t0,0(a0)
nop
bne t0,0,$findz
add a0,1
// go back over null byte
add a0,-1
// start up first word
// adjust pointers so that a0 points to next word
// t7 = a1 adjusted by same amount minus one
// t0,t1,t2,t3 are filled with 4 consecutive bytes
// t4 is filled with the same 4 bytes in a single word
lb t0, 0(a1)
ori t5, a0, 3 # get an early start
beq t0, 0, $doch0
sub t6, t5, a0 # number of char in 1st word of dest - 1
lb t1, 1(a1)
add t7, a1, t6 # offset starting point for source string
beq t1, 0, $doch1
nop
lb t2, 2(a1)
nop
beq t2, 0, $doch2
LWS t4, 0(a1) # safe: always in same word as 0(a1)
lb t3, 3(a1)
LWB t4, 3(a1) # fill out word
beq t3, 0, $doch3
SWS t4, 0(a0) # store entire or part word
addi a0, t5, 1-4 # adjust destination ptr
// inner loop
1: lb t0, 1(t7)
addi t7, 4
beq t0, 0, $doch0
addi a0, 4
lb t1, 1+1-4(t7)
nop
beq t1, 0, $doch1
nop
lb t2, 2+1-4(t7)
nop
beq t2, 0, $doch2
LWS t4, 0+1-4(t7)
lb t3, 3+1-4(t7)
LWB t4, 3+1-4(t7)
bne t3, 0, 1b
sw t4, 0(a0)
j ra
nop
// store four bytes using swl/swr
$doch3: j ra
SWB t4, 3(a0)
// store up to three bytes, a byte at a time.
$doch2: sb t2, 2(a0)
$doch1: sb t1, 1(a0)
$doch0: j ra
sb t0, 0(a0)
.end strcat
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