Annotation of sys/lib/libkern/arch/sparc/umul.S, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: umul.S,v 1.5 2003/06/02 23:28:09 millert Exp $ */
! 2: /* $NetBSD: umul.S,v 1.2 1994/10/26 06:40:10 cgd Exp $ */
! 3:
! 4: /*
! 5: * Copyright (c) 1992, 1993
! 6: * The Regents of the University of California. All rights reserved.
! 7: *
! 8: * This software was developed by the Computer Systems Engineering group
! 9: * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
! 10: * contributed to Berkeley.
! 11: *
! 12: * Redistribution and use in source and binary forms, with or without
! 13: * modification, are permitted provided that the following conditions
! 14: * are met:
! 15: * 1. Redistributions of source code must retain the above copyright
! 16: * notice, this list of conditions and the following disclaimer.
! 17: * 2. Redistributions in binary form must reproduce the above copyright
! 18: * notice, this list of conditions and the following disclaimer in the
! 19: * documentation and/or other materials provided with the distribution.
! 20: * 3. Neither the name of the University nor the names of its contributors
! 21: * may be used to endorse or promote products derived from this software
! 22: * without specific prior written permission.
! 23: *
! 24: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
! 25: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 26: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 27: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
! 28: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 29: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 30: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 31: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 32: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 33: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 34: * SUCH DAMAGE.
! 35: *
! 36: * Header: umul.s,v 1.4 92/06/25 13:24:05 torek Exp
! 37: */
! 38:
! 39: #if defined(LIBC_SCCS) && !defined(lint)
! 40: #ifdef notdef
! 41: .asciz "@(#)umul.s 8.1 (Berkeley) 6/4/93"
! 42: #endif
! 43: .asciz "$OpenBSD: umul.S,v 1.5 2003/06/02 23:28:09 millert Exp $"
! 44: #endif /* LIBC_SCCS and not lint */
! 45:
! 46: /*
! 47: * Unsigned multiply. Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the
! 48: * upper 32 bits of the 64-bit product).
! 49: *
! 50: * This code optimizes short (less than 13-bit) multiplies. Short
! 51: * multiplies require 25 instruction cycles, and long ones require
! 52: * 45 instruction cycles.
! 53: *
! 54: * On return, overflow has occurred (%o1 is not zero) if and only if
! 55: * the Z condition code is clear, allowing, e.g., the following:
! 56: *
! 57: * call .umul
! 58: * nop
! 59: * bnz overflow (or tnz)
! 60: */
! 61:
! 62: #include "DEFS.h"
! 63: FUNC(.umul)
! 64: or %o0, %o1, %o4
! 65: mov %o0, %y ! multiplier -> Y
! 66: andncc %o4, 0xfff, %g0 ! test bits 12..31 of *both* args
! 67: be Lmul_shortway ! if zero, can do it the short way
! 68: andcc %g0, %g0, %o4 ! zero the partial product and clear N and V
! 69:
! 70: /*
! 71: * Long multiply. 32 steps, followed by a final shift step.
! 72: */
! 73: mulscc %o4, %o1, %o4 ! 1
! 74: mulscc %o4, %o1, %o4 ! 2
! 75: mulscc %o4, %o1, %o4 ! 3
! 76: mulscc %o4, %o1, %o4 ! 4
! 77: mulscc %o4, %o1, %o4 ! 5
! 78: mulscc %o4, %o1, %o4 ! 6
! 79: mulscc %o4, %o1, %o4 ! 7
! 80: mulscc %o4, %o1, %o4 ! 8
! 81: mulscc %o4, %o1, %o4 ! 9
! 82: mulscc %o4, %o1, %o4 ! 10
! 83: mulscc %o4, %o1, %o4 ! 11
! 84: mulscc %o4, %o1, %o4 ! 12
! 85: mulscc %o4, %o1, %o4 ! 13
! 86: mulscc %o4, %o1, %o4 ! 14
! 87: mulscc %o4, %o1, %o4 ! 15
! 88: mulscc %o4, %o1, %o4 ! 16
! 89: mulscc %o4, %o1, %o4 ! 17
! 90: mulscc %o4, %o1, %o4 ! 18
! 91: mulscc %o4, %o1, %o4 ! 19
! 92: mulscc %o4, %o1, %o4 ! 20
! 93: mulscc %o4, %o1, %o4 ! 21
! 94: mulscc %o4, %o1, %o4 ! 22
! 95: mulscc %o4, %o1, %o4 ! 23
! 96: mulscc %o4, %o1, %o4 ! 24
! 97: mulscc %o4, %o1, %o4 ! 25
! 98: mulscc %o4, %o1, %o4 ! 26
! 99: mulscc %o4, %o1, %o4 ! 27
! 100: mulscc %o4, %o1, %o4 ! 28
! 101: mulscc %o4, %o1, %o4 ! 29
! 102: mulscc %o4, %o1, %o4 ! 30
! 103: mulscc %o4, %o1, %o4 ! 31
! 104: mulscc %o4, %o1, %o4 ! 32
! 105: mulscc %o4, %g0, %o4 ! final shift
! 106:
! 107:
! 108: /*
! 109: * Normally, with the shift-and-add approach, if both numbers are
! 110: * positive you get the correct result. WIth 32-bit two's-complement
! 111: * numbers, -x is represented as
! 112: *
! 113: * x 32
! 114: * ( 2 - ------ ) mod 2 * 2
! 115: * 32
! 116: * 2
! 117: *
! 118: * (the `mod 2' subtracts 1 from 1.bbbb). To avoid lots of 2^32s,
! 119: * we can treat this as if the radix point were just to the left
! 120: * of the sign bit (multiply by 2^32), and get
! 121: *
! 122: * -x = (2 - x) mod 2
! 123: *
! 124: * Then, ignoring the `mod 2's for convenience:
! 125: *
! 126: * x * y = xy
! 127: * -x * y = 2y - xy
! 128: * x * -y = 2x - xy
! 129: * -x * -y = 4 - 2x - 2y + xy
! 130: *
! 131: * For signed multiplies, we subtract (x << 32) from the partial
! 132: * product to fix this problem for negative multipliers (see mul.s).
! 133: * Because of the way the shift into the partial product is calculated
! 134: * (N xor V), this term is automatically removed for the multiplicand,
! 135: * so we don't have to adjust.
! 136: *
! 137: * But for unsigned multiplies, the high order bit wasn't a sign bit,
! 138: * and the correction is wrong. So for unsigned multiplies where the
! 139: * high order bit is one, we end up with xy - (y << 32). To fix it
! 140: * we add y << 32.
! 141: */
! 142: tst %o1
! 143: bl,a 1f ! if %o1 < 0 (high order bit = 1),
! 144: add %o4, %o0, %o4 ! %o4 += %o0 (add y to upper half)
! 145: 1: rd %y, %o0 ! get lower half of product
! 146: retl
! 147: addcc %o4, %g0, %o1 ! put upper half in place and set Z for %o1==0
! 148:
! 149: Lmul_shortway:
! 150: /*
! 151: * Short multiply. 12 steps, followed by a final shift step.
! 152: * The resulting bits are off by 12 and (32-12) = 20 bit positions,
! 153: * but there is no problem with %o0 being negative (unlike above),
! 154: * and overflow is impossible (the answer is at most 24 bits long).
! 155: */
! 156: mulscc %o4, %o1, %o4 ! 1
! 157: mulscc %o4, %o1, %o4 ! 2
! 158: mulscc %o4, %o1, %o4 ! 3
! 159: mulscc %o4, %o1, %o4 ! 4
! 160: mulscc %o4, %o1, %o4 ! 5
! 161: mulscc %o4, %o1, %o4 ! 6
! 162: mulscc %o4, %o1, %o4 ! 7
! 163: mulscc %o4, %o1, %o4 ! 8
! 164: mulscc %o4, %o1, %o4 ! 9
! 165: mulscc %o4, %o1, %o4 ! 10
! 166: mulscc %o4, %o1, %o4 ! 11
! 167: mulscc %o4, %o1, %o4 ! 12
! 168: mulscc %o4, %g0, %o4 ! final shift
! 169:
! 170: /*
! 171: * %o4 has 20 of the bits that should be in the result; %y has
! 172: * the bottom 12 (as %y's top 12). That is:
! 173: *
! 174: * %o4 %y
! 175: * +----------------+----------------+
! 176: * | -12- | -20- | -12- | -20- |
! 177: * +------(---------+------)---------+
! 178: * -----result-----
! 179: *
! 180: * The 12 bits of %o4 left of the `result' area are all zero;
! 181: * in fact, all top 20 bits of %o4 are zero.
! 182: */
! 183:
! 184: rd %y, %o5
! 185: sll %o4, 12, %o0 ! shift middle bits left 12
! 186: srl %o5, 20, %o5 ! shift low bits right 20
! 187: or %o5, %o0, %o0
! 188: retl
! 189: addcc %g0, %g0, %o1 ! %o1 = zero, and set Z
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