1 /* This file is part of the dynarmic project.
2 * Copyright (c) 2018 MerryMage
3 * SPDX-License-Identifier: 0BSD
4 */
5
6 #include "common/fp/mantissa_util.h"
7 #include "common/fp/unpacked.h"
8 #include "common/u128.h"
9
10 namespace Dynarmic::FP {
11
12 constexpr size_t product_point_position = normalized_point_position * 2;
13
ReduceMantissa(bool sign,int exponent,const u128 & mantissa)14 static FPUnpacked ReduceMantissa(bool sign, int exponent, const u128& mantissa) {
15 constexpr int point_position_correction = normalized_point_position - (product_point_position - 64);
16 // We round-to-odd here when reducing the bitwidth of the mantissa so that subsequent roundings are accurate.
17 return {sign, exponent + point_position_correction, mantissa.upper | static_cast<u64>(mantissa.lower != 0)};
18 }
19
FusedMulAdd(FPUnpacked addend,FPUnpacked op1,FPUnpacked op2)20 FPUnpacked FusedMulAdd(FPUnpacked addend, FPUnpacked op1, FPUnpacked op2) {
21 const bool product_sign = op1.sign != op2.sign;
22 const auto [product_exponent, product_value] = [op1, op2]{
23 int exponent = op1.exponent + op2.exponent;
24 u128 value = Multiply64To128(op1.mantissa, op2.mantissa);
25 if (value.Bit<product_point_position + 1>()) {
26 value = value >> 1;
27 exponent++;
28 }
29 return std::make_tuple(exponent, value);
30 }();
31
32 if (product_value == 0) {
33 return addend;
34 }
35
36 if (addend.mantissa == 0) {
37 return ReduceMantissa(product_sign, product_exponent, product_value);
38 }
39
40 const int exp_diff = product_exponent - addend.exponent;
41
42 if (product_sign == addend.sign) {
43 // Addition
44
45 if (exp_diff <= 0) {
46 // addend > product
47 const u64 result = addend.mantissa + StickyLogicalShiftRight(product_value, normalized_point_position - exp_diff).lower;
48 return FPUnpacked{addend.sign, addend.exponent, result};
49 }
50
51 // addend < product
52 const u128 result = product_value + StickyLogicalShiftRight(addend.mantissa, exp_diff - normalized_point_position);
53 return ReduceMantissa(product_sign, product_exponent, result);
54 }
55
56 // Subtraction
57
58 const u128 addend_long = u128(addend.mantissa) << normalized_point_position;
59
60 bool result_sign;
61 u128 result;
62 int result_exponent;
63
64 if (exp_diff == 0 && product_value > addend_long) {
65 result_sign = product_sign;
66 result_exponent = product_exponent;
67 result = product_value - addend_long;
68 } else if (exp_diff <= 0) {
69 result_sign = !product_sign;
70 result_exponent = addend.exponent;
71 result = addend_long - StickyLogicalShiftRight(product_value, -exp_diff);
72 } else {
73 result_sign = product_sign;
74 result_exponent = product_exponent;
75 result = product_value - StickyLogicalShiftRight(addend_long, exp_diff);
76 }
77
78 if (result.upper == 0) {
79 return FPUnpacked{result_sign, result_exponent, result.lower};
80 }
81
82 const int required_shift = normalized_point_position - Common::HighestSetBit(result.upper);
83 result = result << required_shift;
84 result_exponent -= required_shift;
85 return ReduceMantissa(result_sign, result_exponent, result);
86 }
87
88 } // namespace Dynarmic::FP
89