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+/*
+ * arch/alpha/lib/ev67-strrchr.S
+ * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
+ *
+ * Finds length of a 0-terminated string. Optimized for the
+ * Alpha architecture:
+ *
+ * - memory accessed as aligned quadwords only
+ * - uses bcmpge to compare 8 bytes in parallel
+ *
+ * Much of the information about 21264 scheduling/coding comes from:
+ * Compiler Writer's Guide for the Alpha 21264
+ * abbreviated as 'CWG' in other comments here
+ * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
+ * Scheduling notation:
+ * E - either cluster
+ * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
+ * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
+ */
+
+
+#include <asm/regdef.h>
+
+ .set noreorder
+ .set noat
+
+ .align 4
+ .ent strrchr
+ .globl strrchr
+strrchr:
+ .frame sp, 0, ra
+ .prologue 0
+
+ and a1, 0xff, t2 # E : 00000000000000ch
+ insbl a1, 1, t4 # U : 000000000000ch00
+ insbl a1, 2, t5 # U : 0000000000ch0000
+ ldq_u t0, 0(a0) # L : load first quadword Latency=3
+
+ mov zero, t6 # E : t6 is last match aligned addr
+ or t2, t4, a1 # E : 000000000000chch
+ sll t5, 8, t3 # U : 00000000ch000000
+ mov zero, t8 # E : t8 is last match byte compare mask
+
+ andnot a0, 7, v0 # E : align source addr
+ or t5, t3, t3 # E : 00000000chch0000
+ sll a1, 32, t2 # U : 0000chch00000000
+ sll a1, 48, t4 # U : chch000000000000
+
+ or t4, a1, a1 # E : chch00000000chch
+ or t2, t3, t2 # E : 0000chchchch0000
+ or a1, t2, a1 # E : chchchchchchchch
+ lda t5, -1 # E : build garbage mask
+
+ cmpbge zero, t0, t1 # E : bits set iff byte == zero
+ mskqh t5, a0, t4 # E : Complete garbage mask
+ xor t0, a1, t2 # E : make bytes == c zero
+ cmpbge zero, t4, t4 # E : bits set iff byte is garbage
+
+ cmpbge zero, t2, t3 # E : bits set iff byte == c
+ andnot t1, t4, t1 # E : clear garbage from null test
+ andnot t3, t4, t3 # E : clear garbage from char test
+ bne t1, $eos # U : did we already hit the terminator?
+
+ /* Character search main loop */
+$loop:
+ ldq t0, 8(v0) # L : load next quadword
+ cmovne t3, v0, t6 # E : save previous comparisons match
+ nop # : Latency=2, extra map slot (keep nop with cmov)
+ nop
+
+ cmovne t3, t3, t8 # E : Latency=2, extra map slot
+ nop # : keep with cmovne
+ addq v0, 8, v0 # E :
+ xor t0, a1, t2 # E :
+
+ cmpbge zero, t0, t1 # E : bits set iff byte == zero
+ cmpbge zero, t2, t3 # E : bits set iff byte == c
+ beq t1, $loop # U : if we havnt seen a null, loop
+ nop
+
+ /* Mask out character matches after terminator */
+$eos:
+ negq t1, t4 # E : isolate first null byte match
+ and t1, t4, t4 # E :
+ subq t4, 1, t5 # E : build a mask of the bytes upto...
+ or t4, t5, t4 # E : ... and including the null
+
+ and t3, t4, t3 # E : mask out char matches after null
+ cmovne t3, t3, t8 # E : save it, if match found Latency=2, extra map slot
+ nop # : Keep with cmovne
+ nop
+
+ cmovne t3, v0, t6 # E :
+ nop # : Keep with cmovne
+ /* Locate the address of the last matched character */
+ ctlz t8, t2 # U0 : Latency=3 (0x40 for t8=0)
+ nop
+
+ cmoveq t8, 0x3f, t2 # E : Compensate for case when no match is seen
+ nop # E : hide the cmov latency (2) behind ctlz latency
+ lda t5, 0x3f($31) # E :
+ subq t5, t2, t5 # E : Normalize leading zero count
+
+ addq t6, t5, v0 # E : and add to quadword address
+ ret # L0 : Latency=3
+ nop
+ nop
+
+ .end strrchr