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Diffstat (limited to 'sysdeps/alpha/ffs.S')
-rw-r--r-- | sysdeps/alpha/ffs.S | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/sysdeps/alpha/ffs.S b/sysdeps/alpha/ffs.S new file mode 100644 index 0000000..7676b85 --- /dev/null +++ b/sysdeps/alpha/ffs.S @@ -0,0 +1,71 @@ +/* Copyright (C) 1996 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 Library General Public License as +published by the Free Software Foundation; either version 2 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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +/* Finds the first bit set in an integer. Optimized for the Alpha +architecture. */ + +#include <sysdep.h> +#ifdef __linux__ +# include <alpha/regdef.h> +#else +#include <regdef.h> +#endif + + .set noreorder + .set noat + +ENTRY(ffs) + .prologue 0 + + ldq_u zero, 0(sp) # on the 21064, this helps dual-issuing + addl a0, zero, a0 # the last insn and reduces the stall + negq a0, t0 # due to the srl instruction + and a0, t0, t0 + clr v0 + beq a0, done + + # now do binary search for first non-zero bit + + zapnot t0, 0x03, t2 + addq v0, 16, t3 + cmoveq t2, t3, v0 + + zapnot t0, 0x05, t2 + addq v0, 8, t3 + cmoveq t2, t3, v0 + + srl t0, v0, t0 + addq v0, 1, v0 + + and t0, 0x0f, t2 + addq v0, 4, t3 + cmoveq t2, t3, v0 + + and t0, 0x33, t2 + addq v0, 2, t3 + cmoveq t2, t3, v0 + + and t0, 0x55, t2 + addq v0, 1, t3 + cmoveq t2, t3, v0 + +done: ret + + .end ffs |