chromium / chromiumos / third_party / glibc-ports / refs/heads/factory-1987.B / . / sysdeps / alpha / strlen.S

/* Copyright (C) 1996, 1997, 2003 Free Software Foundation, Inc. | |

Contributed by David Mosberger (davidm@cs.arizona.edu). | |

This file is part of the GNU C Library. | |

The GNU C Library is free software; you can redistribute it and/or | |

modify it under the terms of the GNU Lesser General Public | |

License as published by the Free Software Foundation; either | |

version 2.1 of the License, or (at your option) any later version. | |

The GNU C Library is distributed in the hope that it will be useful, | |

but WITHOUT ANY WARRANTY; without even the implied warranty of | |

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |

Lesser General Public License for more details. | |

You should have received a copy of the GNU Lesser General Public | |

License along with the GNU C Library; if not, write to the Free | |

Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |

02111-1307 USA. */ | |

/* Finds length of a 0-terminated string. Optimized for the Alpha | |

architecture: | |

- 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 8 instructions | |

that the binary search needs). | |

*/ | |

#include <sysdep.h> | |

.set noreorder | |

.set noat | |

ENTRY(strlen) | |

#ifdef PROF | |

ldgp gp, 0(pv) | |

lda AT, _mcount | |

jsr AT, (AT), _mcount | |

.prologue 1 | |

#else | |

.prologue 0 | |

#endif | |

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) | |

libc_hidden_builtin_def (strlen) |