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Daniel Dunbar0868ca62011-03-21 23:30:19 +00001//===-- lib/adddf3.c - Double-precision addition ------------------*- C -*-===//
Stephen Canon5c6d2ec2010-07-01 17:58:24 +00002//
3// The LLVM Compiler Infrastructure
4//
Howard Hinnant9ad441f2010-11-16 22:13:33 +00005// This file is dual licensed under the MIT and the University of Illinois Open
6// Source Licenses. See LICENSE.TXT for details.
Stephen Canon5c6d2ec2010-07-01 17:58:24 +00007//
8//===----------------------------------------------------------------------===//
9//
Daniel Dunbar0868ca62011-03-21 23:30:19 +000010// This file implements double-precision soft-float addition with the IEEE-754
11// default rounding (to nearest, ties to even).
Stephen Canon5c6d2ec2010-07-01 17:58:24 +000012//
13//===----------------------------------------------------------------------===//
Stephen Canone5086322010-07-01 15:52:42 +000014
15#define DOUBLE_PRECISION
16#include "fp_lib.h"
17
Chandler Carruth0193b742012-06-22 21:09:15 +000018ARM_EABI_FNALIAS(dadd, adddf3)
Anton Korobeynikov37b97d12011-04-19 17:51:24 +000019
Anton Korobeynikov1c5f89b2011-04-19 17:52:09 +000020COMPILER_RT_ABI fp_t
21__adddf3(fp_t a, fp_t b) {
Stephen Canone5086322010-07-01 15:52:42 +000022
23 rep_t aRep = toRep(a);
24 rep_t bRep = toRep(b);
25 const rep_t aAbs = aRep & absMask;
26 const rep_t bAbs = bRep & absMask;
27
28 // Detect if a or b is zero, infinity, or NaN.
29 if (aAbs - 1U >= infRep - 1U || bAbs - 1U >= infRep - 1U) {
30
31 // NaN + anything = qNaN
32 if (aAbs > infRep) return fromRep(toRep(a) | quietBit);
33 // anything + NaN = qNaN
34 if (bAbs > infRep) return fromRep(toRep(b) | quietBit);
35
36 if (aAbs == infRep) {
37 // +/-infinity + -/+infinity = qNaN
38 if ((toRep(a) ^ toRep(b)) == signBit) return fromRep(qnanRep);
39 // +/-infinity + anything remaining = +/- infinity
40 else return a;
41 }
42
43 // anything remaining + +/-infinity = +/-infinity
44 if (bAbs == infRep) return b;
45
46 // zero + anything = anything
47 if (!aAbs) {
48 // but we need to get the sign right for zero + zero
49 if (!bAbs) return fromRep(toRep(a) & toRep(b));
50 else return b;
51 }
52
53 // anything + zero = anything
54 if (!bAbs) return a;
55 }
56
57 // Swap a and b if necessary so that a has the larger absolute value.
58 if (bAbs > aAbs) {
59 const rep_t temp = aRep;
60 aRep = bRep;
61 bRep = temp;
62 }
63
64 // Extract the exponent and significand from the (possibly swapped) a and b.
65 int aExponent = aRep >> significandBits & maxExponent;
66 int bExponent = bRep >> significandBits & maxExponent;
67 rep_t aSignificand = aRep & significandMask;
68 rep_t bSignificand = bRep & significandMask;
69
70 // Normalize any denormals, and adjust the exponent accordingly.
71 if (aExponent == 0) aExponent = normalize(&aSignificand);
72 if (bExponent == 0) bExponent = normalize(&bSignificand);
73
74 // The sign of the result is the sign of the larger operand, a. If they
75 // have opposite signs, we are performing a subtraction; otherwise addition.
76 const rep_t resultSign = aRep & signBit;
77 const bool subtraction = (aRep ^ bRep) & signBit;
78
79 // Shift the significands to give us round, guard and sticky, and or in the
80 // implicit significand bit. (If we fell through from the denormal path it
81 // was already set by normalize( ), but setting it twice won't hurt
82 // anything.)
83 aSignificand = (aSignificand | implicitBit) << 3;
84 bSignificand = (bSignificand | implicitBit) << 3;
85
86 // Shift the significand of b by the difference in exponents, with a sticky
87 // bottom bit to get rounding correct.
Joerg Sonnenberger0499b842012-06-18 18:51:13 +000088 const unsigned int align = aExponent - bExponent;
Stephen Canone5086322010-07-01 15:52:42 +000089 if (align) {
90 if (align < typeWidth) {
91 const bool sticky = bSignificand << (typeWidth - align);
92 bSignificand = bSignificand >> align | sticky;
93 } else {
94 bSignificand = 1; // sticky; b is known to be non-zero.
95 }
96 }
97
98 if (subtraction) {
99 aSignificand -= bSignificand;
100
101 // If a == -b, return +zero.
102 if (aSignificand == 0) return fromRep(0);
103
104 // If partial cancellation occured, we need to left-shift the result
105 // and adjust the exponent:
106 if (aSignificand < implicitBit << 3) {
107 const int shift = rep_clz(aSignificand) - rep_clz(implicitBit << 3);
108 aSignificand <<= shift;
109 aExponent -= shift;
110 }
111 }
112
113 else /* addition */ {
114 aSignificand += bSignificand;
115
116 // If the addition carried up, we need to right-shift the result and
117 // adjust the exponent:
118 if (aSignificand & implicitBit << 4) {
119 const bool sticky = aSignificand & 1;
120 aSignificand = aSignificand >> 1 | sticky;
121 aExponent += 1;
122 }
123 }
124
125 // If we have overflowed the type, return +/- infinity:
126 if (aExponent >= maxExponent) return fromRep(infRep | resultSign);
127
128 if (aExponent <= 0) {
129 // Result is denormal before rounding; the exponent is zero and we
130 // need to shift the significand.
131 const int shift = 1 - aExponent;
132 const bool sticky = aSignificand << (typeWidth - shift);
133 aSignificand = aSignificand >> shift | sticky;
134 aExponent = 0;
135 }
136
137 // Low three bits are round, guard, and sticky.
138 const int roundGuardSticky = aSignificand & 0x7;
139
140 // Shift the significand into place, and mask off the implicit bit.
141 rep_t result = aSignificand >> 3 & significandMask;
142
143 // Insert the exponent and sign.
144 result |= (rep_t)aExponent << significandBits;
145 result |= resultSign;
146
147 // Final rounding. The result may overflow to infinity, but that is the
148 // correct result in that case.
149 if (roundGuardSticky > 0x4) result++;
150 if (roundGuardSticky == 0x4) result += result & 1;
151 return fromRep(result);
152}