| /* |
| * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu) |
| * |
| * 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 |
| * - 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). |
| */ |
| |
| .set noreorder |
| .set noat |
| |
| .align 3 |
| |
| .globl strlen |
| .ent strlen |
| strlen: |
| .frame $sp, 0, $26, 0 |
| .prologue 0 |
| |
| ldq_u $1, 0($16) # load first quadword ($16 may be misaligned) |
| lda $2, -1($31) |
| insqh $2, $16, $2 |
| andnot $16, 7, $0 |
| or $2, $1, $1 |
| cmpbge $31, $1, $2 # $2 <- bitmask: bit i == 1 <==> i-th byte == 0 |
| bne $2, found |
| |
| loop: ldq $1, 8($0) |
| addq $0, 8, $0 # addr += 8 |
| nop # helps dual issue last two insns |
| cmpbge $31, $1, $2 |
| beq $2, loop |
| |
| found: blbs $2, done # make aligned case fast |
| negq $2, $3 |
| and $2, $3, $2 |
| |
| and $2, 0x0f, $1 |
| addq $0, 4, $3 |
| cmoveq $1, $3, $0 |
| |
| and $2, 0x33, $1 |
| addq $0, 2, $3 |
| cmoveq $1, $3, $0 |
| |
| and $2, 0x55, $1 |
| addq $0, 1, $3 |
| cmoveq $1, $3, $0 |
| |
| done: subq $0, $16, $0 |
| ret $31, ($26) |
| |
| .end strlen |
