diff options
Diffstat (limited to 'sysdeps/alpha/strlen.S')
| -rw-r--r-- | sysdeps/alpha/strlen.S | 82 |
1 files changed, 40 insertions, 42 deletions
diff --git a/sysdeps/alpha/strlen.S b/sysdeps/alpha/strlen.S index 15c78cde64..9eab707388 100644 --- a/sysdeps/alpha/strlen.S +++ b/sysdeps/alpha/strlen.S @@ -19,52 +19,50 @@ not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ /* Finds length of a 0-terminated string. Optimized for the Alpha -architecture: + architecture: - memory accessed as aligned quadwords only - - uses bcmpge 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). */ + - 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 8 instructions + that the binary search needs). +*/ #include <sysdep.h> - .set noreorder - .set noat + .set noreorder + .set noat ENTRY(strlen) - ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned) - lda t1, -1(zero) - insqh t1, a0, t1 - andnot a0, 7, v0 - or t1, t0, t0 - cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0 - bne t1, found - -loop: ldq t0, 8(v0) - addq v0, 8, v0 # addr += 8 - nop # helps dual issue last two insns - cmpbge zero, t0, t1 - beq t1, loop - -found: blbs t1, done # make aligned case fast - negq t1, t2 - and t1, t2, t1 - - and t1, 0x0f, t0 - addq v0, 4, t2 - cmoveq t0, t2, v0 - - and t1, 0x33, t0 - addq v0, 2, t2 - cmoveq t0, t2, v0 - - and t1, 0x55, t0 - addq v0, 1, t2 - cmoveq t0, t2, v0 - -done: subq v0, a0, v0 - ret - - END(strlen) + ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned) + lda t1, -1(zero) + insqh t1, a0, t1 + andnot a0, 7, v0 + or t1, t0, t0 + nop # dual issue the next two on ev5 + cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0 + bne t1, $found + +$loop: ldq t0, 8(v0) + addq v0, 8, v0 # addr += 8 + cmpbge zero, t0, t1 + beq t1, $loop + +$found: negq t1, t2 # clear all but least set bit + and t1, t2, t1 + + and t1, 0xf0, t2 # binary search for that set bit + and t1, 0xcc, t3 + and t1, 0xaa, t4 + cmovne t2, 4, t2 + cmovne t3, 2, t3 + cmovne t4, 1, t4 + addq t2, t3, t2 + addq v0, t4, v0 + addq v0, t2, v0 + nop # dual issue next two on ev4 and ev5 + + subq v0, a0, v0 + ret + + END(strlen) |