88 строки
2.7 KiB
ArmAsm
88 строки
2.7 KiB
ArmAsm
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/*
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* arch/alpha/lib/strrchr.S
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* Contributed by Richard Henderson (rth@tamu.edu)
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*
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* Return the address of the last occurrence of a given character
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* within a null-terminated string, or null if it is not found.
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*/
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#include <asm/regdef.h>
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.set noreorder
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.set noat
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.align 3
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.ent strrchr
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.globl strrchr
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strrchr:
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.frame sp, 0, ra
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.prologue 0
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zapnot a1, 1, a1 # e0 : zero extend our test character
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mov zero, t6 # .. e1 : t6 is last match aligned addr
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sll a1, 8, t5 # e0 : replicate our test character
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mov zero, t8 # .. e1 : t8 is last match byte compare mask
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or t5, a1, a1 # e0 :
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ldq_u t0, 0(a0) # .. e1 : load first quadword
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sll a1, 16, t5 # e0 :
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andnot a0, 7, v0 # .. e1 : align source addr
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or t5, a1, a1 # e0 :
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lda t4, -1 # .. e1 : build garbage mask
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sll a1, 32, t5 # e0 :
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cmpbge zero, t0, t1 # .. e1 : bits set iff byte == zero
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mskqh t4, a0, t4 # e0 :
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or t5, a1, a1 # .. e1 : character replication complete
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xor t0, a1, t2 # e0 : make bytes == c zero
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cmpbge zero, t4, t4 # .. e1 : bits set iff byte is garbage
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cmpbge zero, t2, t3 # e0 : bits set iff byte == c
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andnot t1, t4, t1 # .. e1 : clear garbage from null test
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andnot t3, t4, t3 # e0 : clear garbage from char test
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bne t1, $eos # .. e1 : did we already hit the terminator?
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/* Character search main loop */
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$loop:
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ldq t0, 8(v0) # e0 : load next quadword
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cmovne t3, v0, t6 # .. e1 : save previous comparisons match
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cmovne t3, t3, t8 # e0 :
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addq v0, 8, v0 # .. e1 :
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xor t0, a1, t2 # e0 :
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cmpbge zero, t0, t1 # .. e1 : bits set iff byte == zero
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cmpbge zero, t2, t3 # e0 : bits set iff byte == c
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beq t1, $loop # .. e1 : if we havnt seen a null, loop
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/* Mask out character matches after terminator */
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$eos:
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negq t1, t4 # e0 : isolate first null byte match
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and t1, t4, t4 # e1 :
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subq t4, 1, t5 # e0 : build a mask of the bytes upto...
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or t4, t5, t4 # e1 : ... and including the null
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and t3, t4, t3 # e0 : mask out char matches after null
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cmovne t3, t3, t8 # .. e1 : save it, if match found
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cmovne t3, v0, t6 # e0 :
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/* Locate the address of the last matched character */
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/* Retain the early exit for the ev4 -- the ev5 mispredict penalty
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is 5 cycles -- the same as just falling through. */
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beq t8, $retnull # .. e1 :
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and t8, 0xf0, t2 # e0 : binary search for the high bit set
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cmovne t2, t2, t8 # .. e1 (zdb)
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cmovne t2, 4, t2 # e0 :
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and t8, 0xcc, t1 # .. e1 :
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cmovne t1, t1, t8 # e0 :
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cmovne t1, 2, t1 # .. e1 :
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and t8, 0xaa, t0 # e0 :
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cmovne t0, 1, t0 # .. e1 (zdb)
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addq t2, t1, t1 # e0 :
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addq t6, t0, v0 # .. e1 : add our aligned base ptr to the mix
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addq v0, t1, v0 # e0 :
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ret # .. e1 :
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$retnull:
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mov zero, v0 # e0 :
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ret # .. e1 :
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.end strrchr
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