Annotation of sys/lib/libkern/arch/alpha/ffs.S, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: ffs.S,v 1.1 1996/10/31 00:43:18 niklas Exp $ */
2: /* $NetBSD: ffs.S,v 1.3 1996/10/17 04:26:26 cgd Exp $ */
3:
4: /*
5: * Copyright (c) 1995 Christopher G. Demetriou
6: * All rights reserved.
7: *
8: * Redistribution and use in source and binary forms, with or without
9: * modification, are permitted provided that the following conditions
10: * are met:
11: * 1. Redistributions of source code must retain the above copyright
12: * notice, this list of conditions and the following disclaimer.
13: * 2. Redistributions in binary form must reproduce the above copyright
14: * notice, this list of conditions and the following disclaimer in the
15: * documentation and/or other materials provided with the distribution.
16: * 3. All advertising materials mentioning features or use of this software
17: * must display the following acknowledgement:
18: * This product includes software developed by Christopher G. Demetriou
19: * for the NetBSD Project.
20: * 4. The name of the author may not be used to endorse or promote products
21: * derived from this software without specific prior written permission
22: *
23: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
24: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
25: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
26: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
27: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
28: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
29: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
30: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
31: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
32: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
33: */
34:
35: #include <machine/asm.h>
36:
37: LEAF(ffs, 1)
38: addl a0, 0, t0
39: beq t0, Lallzero
40:
41: /*
42: * Initialize return value (v0), and set up t1 so that it
43: * contains the mask with only the lowest bit set.
44: */
45: subl zero, t0, t1
46: ldil v0, 1
47: and t0, t1, t1
48:
49: and t1, 0xff, t2
50: bne t2, Ldo8
51:
52: /*
53: * If lower 16 bits empty, add 16 to result and use upper 16.
54: */
55: zapnot t1, 0x03, t3
56: bne t3, Ldo16
57: sra t1, 16, t1
58: addl v0, 16, v0
59:
60: Ldo16:
61: /*
62: * If lower 8 bits empty, add 8 to result and use upper 8.
63: */
64: and t1, 0xff, t4
65: bne t4, Ldo8
66: sra t1, 8, t1
67: addl v0, 8, v0
68:
69: Ldo8:
70: and t1, 0x0f, t5 /* lower 4 of 8 empty? */
71: and t1, 0x33, t6 /* lower 2 of each 4 empty? */
72: and t1, 0x55, t7 /* lower 1 of each 2 empty? */
73:
74: /* If lower 4 bits empty, add 4 to result. */
75: bne t5, Ldo4
76: addl v0, 4, v0
77:
78: Ldo4: /* If lower 2 bits of each 4 empty, add 2 to result. */
79: bne t6, Ldo2
80: addl v0, 2, v0
81:
82: Ldo2: /* If lower bit of each 2 empty, add 1 to result. */
83: bne t7, Ldone
84: addl v0, 1, v0
85:
86: Ldone:
87: RET
88:
89: Lallzero:
90: bis zero, zero, v0
91: RET
92: END(ffs)
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