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+/*
+ * arch/alpha/lib/ev67-strlen.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
+ */
+
+ .set noreorder
+ .set noat
+
+ .globl strlen
+ .ent strlen
+ .align 4
+strlen:
+ ldq_u $1, 0($16) # L : load first quadword ($16 may be misaligned)
+ lda $2, -1($31) # E :
+ insqh $2, $16, $2 # U :
+ andnot $16, 7, $0 # E :
+
+ or $2, $1, $1 # E :
+ cmpbge $31, $1, $2 # E : $2 <- bitmask: bit i == 1 <==> i-th byte == 0
+ nop # E :
+ bne $2, $found # U :
+
+$loop: ldq $1, 8($0) # L :
+ addq $0, 8, $0 # E : addr += 8
+ cmpbge $31, $1, $2 # E :
+ beq $2, $loop # U :
+
+$found:
+ cttz $2, $3 # U0 :
+ addq $0, $3, $0 # E :
+ subq $0, $16, $0 # E :
+ ret $31, ($26) # L0 :
+
+ .end strlen