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+/*
+ * arch/alpha/lib/ev6-memchr.S
+ *
+ * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
+ *
+ * Finds characters in a memory area. Optimized for the Alpha:
+ *
+ * - memory accessed as aligned quadwords only
+ * - uses cmpbge to compare 8 bytes in parallel
+ * - does binary search to find 0 byte in last
+ * quadword (HAKMEM needed 12 instructions to
+ * do this instead of the 9 instructions that
+ * binary search needs).
+ *
+ * For correctness consider that:
+ *
+ * - only minimum number of quadwords may be accessed
+ * - the third argument is an unsigned long
+ *
+ * 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
+ * Try not to change the actual algorithm if possible for consistency.
+ */
+
+ .set noreorder
+ .set noat
+
+ .align 4
+ .globl memchr
+ .ent memchr
+memchr:
+ .frame $30,0,$26,0
+ .prologue 0
+
+ # Hack -- if someone passes in (size_t)-1, hoping to just
+ # search til the end of the address space, we will overflow
+ # below when we find the address of the last byte. Given
+ # that we will never have a 56-bit address space, cropping
+ # the length is the easiest way to avoid trouble.
+ zap $18, 0x80, $5 # U : Bound length
+ beq $18, $not_found # U :
+ ldq_u $1, 0($16) # L : load first quadword Latency=3
+ and $17, 0xff, $17 # E : L L U U : 00000000000000ch
+
+ insbl $17, 1, $2 # U : 000000000000ch00
+ cmpult $18, 9, $4 # E : small (< 1 quad) string?
+ or $2, $17, $17 # E : 000000000000chch
+ lda $3, -1($31) # E : U L L U
+
+ sll $17, 16, $2 # U : 00000000chch0000
+ addq $16, $5, $5 # E : Max search address
+ or $2, $17, $17 # E : 00000000chchchch
+ sll $17, 32, $2 # U : U L L U : chchchch00000000
+
+ or $2, $17, $17 # E : chchchchchchchch
+ extql $1, $16, $7 # U : $7 is upper bits
+ beq $4, $first_quad # U :
+ ldq_u $6, -1($5) # L : L U U L : eight or less bytes to search Latency=3
+
+ extqh $6, $16, $6 # U : 2 cycle stall for $6
+ mov $16, $0 # E :
+ nop # E :
+ or $7, $6, $1 # E : L U L U $1 = quadword starting at $16
+
+ # Deal with the case where at most 8 bytes remain to be searched
+ # in $1. E.g.:
+ # $18 = 6
+ # $1 = ????c6c5c4c3c2c1
+$last_quad:
+ negq $18, $6 # E :
+ xor $17, $1, $1 # E :
+ srl $3, $6, $6 # U : $6 = mask of $18 bits set
+ cmpbge $31, $1, $2 # E : L U L U
+
+ nop
+ nop
+ and $2, $6, $2 # E :
+ beq $2, $not_found # U : U L U L
+
+$found_it:
+#if defined(__alpha_fix__) && defined(__alpha_cix__)
+ /*
+ * Since we are guaranteed to have set one of the bits, we don't
+ * have to worry about coming back with a 0x40 out of cttz...
+ */
+ cttz $2, $3 # U0 :
+ addq $0, $3, $0 # E : All done
+ nop # E :
+ ret # L0 : L U L U
+#else
+ /*
+ * Slow and clunky. It can probably be improved.
+ * An exercise left for others.
+ */
+ negq $2, $3 # E :
+ and $2, $3, $2 # E :
+ and $2, 0x0f, $1 # E :
+ addq $0, 4, $3 # E :
+
+ cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
+ nop # E : keep with cmov
+ and $2, 0x33, $1 # E :
+ addq $0, 2, $3 # E : U L U L : 2 cycle stall on $0
+
+ cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
+ nop # E : keep with cmov
+ and $2, 0x55, $1 # E :
+ addq $0, 1, $3 # E : U L U L : 2 cycle stall on $0
+
+ cmoveq $1, $3, $0 # E : Latency 2, extra map cycle
+ nop
+ nop
+ ret # L0 : L U L U
+#endif
+
+ # Deal with the case where $18 > 8 bytes remain to be
+ # searched. $16 may not be aligned.
+ .align 4
+$first_quad:
+ andnot $16, 0x7, $0 # E :
+ insqh $3, $16, $2 # U : $2 = 0000ffffffffffff ($16<0:2> ff)
+ xor $1, $17, $1 # E :
+ or $1, $2, $1 # E : U L U L $1 = ====ffffffffffff
+
+ cmpbge $31, $1, $2 # E :
+ bne $2, $found_it # U :
+ # At least one byte left to process.
+ ldq $1, 8($0) # L :
+ subq $5, 1, $18 # E : U L U L
+
+ addq $0, 8, $0 # E :
+ # Make $18 point to last quad to be accessed (the
+ # last quad may or may not be partial).
+ andnot $18, 0x7, $18 # E :
+ cmpult $0, $18, $2 # E :
+ beq $2, $final # U : U L U L
+
+ # At least two quads remain to be accessed.
+
+ subq $18, $0, $4 # E : $4 <- nr quads to be processed
+ and $4, 8, $4 # E : odd number of quads?
+ bne $4, $odd_quad_count # U :
+ # At least three quads remain to be accessed
+ mov $1, $4 # E : L U L U : move prefetched value to correct reg
+
+ .align 4
+$unrolled_loop:
+ ldq $1, 8($0) # L : prefetch $1
+ xor $17, $4, $2 # E :
+ cmpbge $31, $2, $2 # E :
+ bne $2, $found_it # U : U L U L
+
+ addq $0, 8, $0 # E :
+ nop # E :
+ nop # E :
+ nop # E :
+
+$odd_quad_count:
+ xor $17, $1, $2 # E :
+ ldq $4, 8($0) # L : prefetch $4
+ cmpbge $31, $2, $2 # E :
+ addq $0, 8, $6 # E :
+
+ bne $2, $found_it # U :
+ cmpult $6, $18, $6 # E :
+ addq $0, 8, $0 # E :
+ nop # E :
+
+ bne $6, $unrolled_loop # U :
+ mov $4, $1 # E : move prefetched value into $1
+ nop # E :
+ nop # E :
+
+$final: subq $5, $0, $18 # E : $18 <- number of bytes left to do
+ nop # E :
+ nop # E :
+ bne $18, $last_quad # U :
+
+$not_found:
+ mov $31, $0 # E :
+ nop # E :
+ nop # E :
+ ret # L0 :
+
+ .end memchr