zhlee_memcpy.s

memcpy函数优化代码,使用汇编实现,可提高memcpy的实现性能.

#define ENTRY(_LABEL) \\
 .global _LABEL; _LABEL:

.globl zhleememcpy
zhleememcpy:

/*ENTRY(memcpy)
*/
stmfd sp!, {r0, r12, lr}
bl _zhleememcpy
ldmfd sp!, {r0, r12, pc}
 
 

.globl zhleememove
zhleememmove:
/*
ENTRY(memmove)
*/
stmfd sp!, {r0, r12, lr}
bl _zhleememcpy
ldmfd sp!, {r0, r12, pc}
 
 
 
/*
* This is one fun bit of code ...
* Some easy listening music is suggested while trying to understand this
* code e.g. Iron Maiden
*
* For anyone attempting to understand it :
*
* The core code is implemented here with simple stubs for memcpy()
* memmove() and bcopy().
*
* All local labels are prefixed with Lmemcpy_
* Following the prefix a label starting f is used in the forward copy code
* while a label using b is used in the backwards copy code
* The source and destination addresses determine whether a forward or
* backward copy is performed.
* Separate bits of code are used to deal with the following situations
* for both the forward and backwards copy.
* unaligned source address
* unaligned destination address
* Separate copy routines are used to produce an optimised result for each
* of these cases.
* The copy code will use LDM/STM instructions to copy up to 32 bytes at
* a time where possible.
*
* Note: r12 (aka ip) can be trashed during the function along with
* r0-r3 although r0-r2 have defined uses i.e. src, dest, len through out.
* Additional registers are preserved prior to use i.e. r4, r5 & lr
*
* Apologies for the state of the comments;-)
*/
 
 
_zhleememcpy:
/*
ENTRY(_memcpy)
*/
/* Determine copy direction */
cmp r1, r0
bcc Lmemcpy_backwards
 
moveq r0, #0   /* Quick abort for len=0 */
moveq pc, lr
 
stmdb sp!, {r0, lr}  /* memcpy() returns dest addr */
subs r2, r2, #4
blt Lmemcpy_fl4  /* less than 4 bytes */
ands r12, r0, #3
bne Lmemcpy_fdestul  /* oh unaligned destination addr */
ands r12, r1, #3
bne Lmemcpy_fsrcul  /* oh unaligned source addr */
 
Lmemcpy_ft8:
/* We have aligned source and destination */
subs r2, r2, #8
blt Lmemcpy_fl12  /* less than 12 bytes (4 from above) */
subs r2, r2, #0x14        
blt Lmemcpy_fl32  /* less than 32 bytes (12 from above) */
stmdb sp!, {r4}  /* borrow r4 */
 
/* blat 32 bytes at a time */
/* XXX for really big copies perhaps we should use more registers */
Lmemcpy_floop32:
ldmia r1!, {r3, r4, r12, lr}
stmia r0!, {r3, r4, r12, lr}
ldmia r1!, {r3, r4, r12, lr}
stmia r0!, {r3, r4, r12, lr}
subs r2, r2, #0x20        
bge Lmemcpy_floop32
 
cmn r2, #0x10
ldmgeia r1!, {r3, r4, r12, lr} /* blat a remaining 16 bytes */
stmgeia r0!, {r3, r4, r12, lr}
subge r2, r2, #0x10        
ldmia sp!, {r4}  /* return r4 */
 
Lmemcpy_fl32:
adds r2, r2, #0x14        
 
/* blat 12 bytes at a time */
Lmemcpy_floop12:
ldmgeia r1!, {r3, r12, lr}
stmgeia r0!, {r3, r12, lr}
subges r2, r2, #0x0c        
bge Lmemcpy_floop12
 
Lmemcpy_fl12:
adds r2, r2, #8
blt Lmemcpy_fl4
 
subs r2, r2, #4
ldrlt r3, [r1], #4
strlt r3, [r0], #4
ldmgeia r1!, {r3, r12}
stmgeia r0!, {r3, r12}
subge r2, r2, #4
 
Lmemcpy_fl4:
/* less than 4 bytes to go */
adds r2, r2, #4
ldmeqia sp!, {r0, pc}  /* done */
 
/* copy the crud byte at a time */
cmp r2, #2
ldrb r3, [r1], #1
strb r3, [r0], #1
ldrgeb r3, [r1], #1
strgeb r3, [r0], #1
ldrgtb r3, [r1], #1
strgtb r3, [r0], #1
ldmia sp!, {r0, pc}
 
/* erg - unaligned destination */
Lmemcpy_fdestul:
rsb r12, r12, #4
cmp r12, #2
 
/* align destination with byte copies */
ldrb r3, [r1], #1
strb r3, [r0], #1
ldrgeb r3, [r1], #1
strgeb r3, [r0], #1
ldrgtb r3, [r1], #1
strgtb r3, [r0], #1
subs r2, r2, r12
blt Lmemcpy_fl4  /* less the 4 bytes */
 
ands r12, r1, #3
beq Lmemcpy_ft8  /* we have an aligned source */
 
/* erg - unaligned source */
/* This is where it gets nasty ... */
Lmemcpy_fsrcul:
bic r1, r1, #3
ldr lr, [r1], #4
cmp r12, #2
bgt Lmemcpy_fsrcul3
beq Lmemcpy_fsrcul2
cmp r2, #0x0c            
blt Lmemcpy_fsrcul1loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5}
 
Lmemcpy_fsrcul1loop16:
mov r3, lr, lsr #8
ldmia r1!, {r4, r5, r12, lr}
orr r3, r3, r4, lsl #24
mov r4, r4, lsr #8
orr r4, r4, r5, lsl #24
mov r5, r5, lsr #8
orr r5, r5, r12, lsl #24
mov r12, r12, lsr #8
orr r12, r12, lr, lsl #24
stmia r0!, {r3-r5, r12}
subs r2, r2, #0x10        
bge Lmemcpy_fsrcul1loop16
ldmia sp!, {r4, r5}
adds r2, r2, #0x0c        
blt Lmemcpy_fsrcul1l4
 
Lmemcpy_fsrcul1loop4:
mov r12, lr, lsr #8
ldr lr, [r1], #4
orr r12, r12, lr, lsl #24
str r12, [r0], #4
subs r2, r2, #4
bge Lmemcpy_fsrcul1loop4
 
Lmemcpy_fsrcul1l4:
sub r1, r1, #3
b Lmemcpy_fl4
 
Lmemcpy_fsrcul2:
cmp r2, #0x0c            
blt Lmemcpy_fsrcul2loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5}
 
Lmemcpy_fsrcul2loop16:
mov r3, lr, lsr #16
ldmia r1!, {r4, r5, r12, lr}
orr r3, r3, r4, lsl #16
mov r4, r4, lsr #16
orr r4, r4, r5, lsl #16
mov r5, r5, lsr #16
orr r5, r5, r12, lsl #16
mov r12, r12, lsr #16
orr r12, r12, lr, lsl #16
stmia r0!, {r3-r5, r12}
subs r2, r2, #0x10        
bge Lmemcpy_fsrcul2loop16
ldmia sp!, {r4, r5}
adds r2, r2, #0x0c        
blt Lmemcpy_fsrcul2l4
 
Lmemcpy_fsrcul2loop4:
mov r12, lr, lsr #16
ldr lr, [r1], #4
orr r12, r12, lr, lsl #16
str r12, [r0], #4
subs r2, r2, #4
bge Lmemcpy_fsrcul2loop4
 
Lmemcpy_fsrcul2l4:
sub r1, r1, #2
b Lmemcpy_fl4
 
Lmemcpy_fsrcul3:
cmp r2, #0x0c            
blt Lmemcpy_fsrcul3loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5}
 
Lmemcpy_fsrcul3loop16:
mov r3, lr, lsr #24
ldmia r1!, {r4, r5, r12, lr}
orr r3, r3, r4, lsl #8
mov r4, r4, lsr #24
orr r4, r4, r5, lsl #8
mov r5, r5, lsr #24
orr r5, r5, r12, lsl #8
mov r12, r12, lsr #24
orr r12, r12, lr, lsl #8
stmia r0!, {r3-r5, r12}
subs r2, r2, #0x10        
bge Lmemcpy_fsrcul3loop16
ldmia sp!, {r4, r5}
adds r2, r2, #0x0c        
blt Lmemcpy_fsrcul3l4
 
Lmemcpy_fsrcul3loop4:
mov r12, lr, lsr #24
ldr lr, [r1], #4
orr r12, r12, lr, lsl #8
str r12, [r0], #4
subs r2, r2, #4
bge Lmemcpy_fsrcul3loop4
 
Lmemcpy_fsrcul3l4:
sub r1, r1, #1
b Lmemcpy_fl4
 
Lmemcpy_backwards:
add r1, r1, r2
add r0, r0, r2
subs r2, r2, #4
blt Lmemcpy_bl4  /* less than 4 bytes */
ands r12, r0, #3
bne Lmemcpy_bdestul  /* oh unaligned destination addr */
ands r12, r1, #3
bne Lmemcpy_bsrcul  /* oh unaligned source addr */
 
Lmemcpy_bt8:
/* We have aligned source and destination */
subs r2, r2, #8
blt Lmemcpy_bl12  /* less than 12 bytes (4 from above) */
stmdb sp!, {r4, lr}
subs r2, r2, #0x14  /* less than 32 bytes (12 from above) */
blt Lmemcpy_bl32
 
/* blat 32 bytes at a time */
/* XXX for really big copies perhaps we should use more registers */
Lmemcpy_bloop32:
ldmdb r1!, {r3, r4, r12, lr}
stmdb r0!, {r3, r4, r12, lr}
ldmdb r1!, {r3, r4, r12, lr}
stmdb r0!, {r3, r4, r12, lr}
subs r2, r2, #0x20        
bge Lmemcpy_bloop32
 
Lmemcpy_bl32:
cmn r2, #0x10            
ldmgedb r1!, {r3, r4, r12, lr} /* blat a remaining 16 bytes */
stmgedb r0!, {r3, r4, r12, lr}
subge r2, r2, #0x10        
adds r2, r2, #0x14        
ldmgedb r1!, {r3, r12, lr} /* blat a remaining 12 bytes */
stmgedb r0!, {r3, r12, lr}
subge r2, r2, #0x0c        
ldmia sp!, {r4, lr}
 
Lmemcpy_bl12:
adds r2, r2, #8
blt Lmemcpy_bl4
subs r2, r2, #4
ldrlt r3, [r1, #-4]!
strlt r3, [r0, #-4]!
ldmgedb r1!, {r3, r12}
stmgedb r0!, {r3, r12}
subge r2, r2, #4
 
Lmemcpy_bl4:
/* less than 4 bytes to go */
adds r2, r2, #4
moveq pc, lr   /* done */
 
/* copy the crud byte at a time */
cmp r2, #2
ldrb r3, [r1, #-1]!
strb r3, [r0, #-1]!
ldrgeb r3, [r1, #-1]!
strgeb r3, [r0, #-1]!
ldrgtb r3, [r1, #-1]!
strgtb r3, [r0, #-1]!
mov pc, lr
 
/* erg - unaligned destination */
Lmemcpy_bdestul:
cmp r12, #2
 
/* align destination with byte copies */
ldrb r3, [r1, #-1]!
strb r3, [r0, #-1]!
ldrgeb r3, [r1, #-1]!
strgeb r3, [r0, #-1]!
ldrgtb r3, [r1, #-1]!
strgtb r3, [r0, #-1]!
subs r2, r2, r12
blt Lmemcpy_bl4  /* less than 4 bytes to go */
ands r12, r1, #3
beq Lmemcpy_bt8  /* we have an aligned source */
 
/* erg - unaligned source */
/* This is where it gets nasty ... */
Lmemcpy_bsrcul:
bic r1, r1, #3
ldr r3, [r1, #0]
cmp r12, #2
blt Lmemcpy_bsrcul1
beq Lmemcpy_bsrcul2
cmp r2, #0x0c            
blt Lmemcpy_bsrcul3loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5, lr}
 
Lmemcpy_bsrcul3loop16:
mov lr, r3, lsl #8
ldmdb r1!, {r3-r5, r12}
orr lr, lr, r12, lsr #24
mov r12, r12, lsl #8
orr r12, r12, r5, lsr #24
mov r5, r5, lsl #8
orr r5, r5, r4, lsr #24
mov r4, r4, lsl #8
orr r4, r4, r3, lsr #24
stmdb r0!, {r4, r5, r12, lr}
subs r2, r2, #0x10        
bge Lmemcpy_bsrcul3loop16
ldmia sp!, {r4, r5, lr}
adds r2, r2, #0x0c        
blt Lmemcpy_bsrcul3l4
 
Lmemcpy_bsrcul3loop4:
mov r12, r3, lsl #8
ldr r3, [r1, #-4]!
orr r12, r12, r3, lsr #24
str r12, [r0, #-4]!
subs r2, r2, #4
bge Lmemcpy_bsrcul3loop4
 
Lmemcpy_bsrcul3l4:
add r1, r1, #3
b Lmemcpy_bl4
 
Lmemcpy_bsrcul2:
cmp r2, #0x0c            
blt Lmemcpy_bsrcul2loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5, lr}
 
Lmemcpy_bsrcul2loop16:
mov lr, r3, lsl #16
ldmdb r1!, {r3-r5, r12}
orr lr, lr, r12, lsr #16
mov r12, r12, lsl #16
orr r12, r12, r5, lsr #16
mov r5, r5, lsl #16
orr r5, r5, r4, lsr #16
mov r4, r4, lsl #16
orr r4, r4, r3, lsr #16
stmdb r0!, {r4, r5, r12, lr}
subs r2, r2, #0x10        
bge Lmemcpy_bsrcul2loop16
ldmia sp!, {r4, r5, lr}
adds r2, r2, #0x0c        
blt Lmemcpy_bsrcul2l4
 
Lmemcpy_bsrcul2loop4:
mov r12, r3, lsl #16
ldr r3, [r1, #-4]!
orr r12, r12, r3, lsr #16
str r12, [r0, #-4]!
subs r2, r2, #4
bge Lmemcpy_bsrcul2loop4
 
Lmemcpy_bsrcul2l4:
add r1, r1, #2
b Lmemcpy_bl4
 
Lmemcpy_bsrcul1:
cmp r2, #0x0c            
blt Lmemcpy_bsrcul1loop4
sub r2, r2, #0x0c        
stmdb sp!, {r4, r5, lr}
 
Lmemcpy_bsrcul1loop32:
mov lr, r3, lsl #24
ldmdb r1!, {r3-r5, r12}
orr lr, lr, r12, lsr #8
mov r12, r12, lsl #24
orr r12, r12, r5, lsr #8
mov r5, r5, lsl #24
orr r5, r5, r4, lsr #8
mov r4, r4, lsl #24
orr r4, r4, r3, lsr #8
stmdb r0!, {r4, r5, r12, lr}
subs r2, r2, #0x10        
bge Lmemcpy_bsrcul1loop32
ldmia sp!, {r4, r5, lr}
adds r2, r2, #0x0c        
blt Lmemcpy_bsrcul1l4
 
Lmemcpy_bsrcul1loop4:
mov r12, r3, lsl #24
ldr r3, [r1, #-4]!
orr r12, r12, r3, lsr #8
str r12, [r0, #-4]!
subs r2, r2, #4
bge Lmemcpy_bsrcul1loop4
 
Lmemcpy_bsrcul1l4:
add r1, r1, #1
b Lmemcpy_bl4