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Diffstat (limited to 'arch/alpha/lib/ev6-memchr.S')
| -rw-r--r-- | arch/alpha/lib/ev6-memchr.S | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/arch/alpha/lib/ev6-memchr.S b/arch/alpha/lib/ev6-memchr.S new file mode 100644 index 000000000..56bf9e14e --- /dev/null +++ b/arch/alpha/lib/ev6-memchr.S @@ -0,0 +1,193 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * 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. + */ +#include <asm/export.h> + .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: +#ifdef CONFIG_ALPHA_EV67 + /* + * 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 + EXPORT_SYMBOL(memchr) |