From 8f75a1fe04f5b8c40d044d03b965b89b4c73941a Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Thu, 26 Jul 2018 10:59:33 +0100
Subject: [PATCH] fp/info: Replace constant value generators with FPValue

Instead of having multiple different functions we can just have one.
---
 src/common/fp/info.h                  | 25 +++++++++++++++++++++----
 src/common/fp/op/FPRSqrtStepFused.cpp |  3 ++-
 src/common/fp/op/FPRecipStepFused.cpp |  3 ++-
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/common/fp/info.h b/src/common/fp/info.h
index b78f1382..df3de71f 100644
--- a/src/common/fp/info.h
+++ b/src/common/fp/info.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include "common/bit_util.h"
 #include "common/common_types.h"
 
 namespace Dynarmic::FP {
@@ -33,8 +34,6 @@ struct FPInfo<u32> {
     static constexpr u32 Infinity(bool sign) { return exponent_mask | Zero(sign); }
     static constexpr u32 MaxNormal(bool sign) { return (exponent_mask - 1) | Zero(sign); }
     static constexpr u32 DefaultNaN() { return exponent_mask | (u32(1) << (explicit_mantissa_width - 1)); }
-    static constexpr u32 OnePointFive(bool sign) { return Zero(sign) | (u32(1) << (explicit_mantissa_width - 1)) | (u32(exponent_bias) << explicit_mantissa_width); }
-    static constexpr u32 Two(bool sign) { return Zero(sign) | (u32(exponent_bias + 1) << explicit_mantissa_width); }
 };
 
 template<>
@@ -57,8 +56,26 @@ struct FPInfo<u64> {
     static constexpr u64 Infinity(bool sign) { return exponent_mask | Zero(sign); }
     static constexpr u64 MaxNormal(bool sign) { return (exponent_mask - 1) | Zero(sign); }
     static constexpr u64 DefaultNaN() { return exponent_mask | (u64(1) << (explicit_mantissa_width - 1)); }
-    static constexpr u64 OnePointFive(bool sign) { return Zero(sign) | (u64(1) << (explicit_mantissa_width - 1)) | (u64(exponent_bias) << explicit_mantissa_width); }
-    static constexpr u64 Two(bool sign) { return Zero(sign) | (u64(exponent_bias + 1) << explicit_mantissa_width); }
 };
 
+/// value = (sign ? -1 : +1) * 2^exponent * value
+/// @note We do not handle denormals. Denormals will static_assert.
+template<typename FPT, bool sign, int exponent, FPT value>
+constexpr FPT FPValue() {
+    if constexpr (value == 0) {
+        return FPInfo<FPT>::Zero(sign);
+    }
+
+    constexpr int point_position = static_cast<int>(FPInfo<FPT>::mantissa_width);
+    constexpr int highest_bit = Common::HighestSetBit(value);
+    constexpr int offset = point_position - highest_bit;
+    constexpr int normalized_exponent = exponent - offset + point_position;
+    static_assert(offset >= 0);
+    static_assert(normalized_exponent >= FPInfo<FPT>::exponent_min && normalized_exponent <= FPInfo<FPT>::exponent_max);
+
+    constexpr FPT mantissa = (value << offset) & FPInfo<FPT>::mantissa_mask;
+    constexpr FPT biased_exponent = static_cast<FPT>(normalized_exponent + FPInfo<FPT>::exponent_bias);
+    return FPInfo<FPT>::Zero(sign) | mantissa | (biased_exponent << FPInfo<FPT>::explicit_mantissa_width);
+}
+
 } // namespace Dynarmic::FP 
diff --git a/src/common/fp/op/FPRSqrtStepFused.cpp b/src/common/fp/op/FPRSqrtStepFused.cpp
index e83db7b2..5e5ab742 100644
--- a/src/common/fp/op/FPRSqrtStepFused.cpp
+++ b/src/common/fp/op/FPRSqrtStepFused.cpp
@@ -33,7 +33,8 @@ FPT FPRSqrtStepFused(FPT op1, FPT op2, FPCR fpcr, FPSR& fpsr) {
     const bool zero2 = type2 == FPType::Zero;
 
     if ((inf1 && zero2) || (zero1 && inf2)) {
-        return FPInfo<FPT>::OnePointFive(false);
+        // return +1.5
+        return FPValue<FPT, false, -1, 3>();
     }
 
     if (inf1 || inf2) {
diff --git a/src/common/fp/op/FPRecipStepFused.cpp b/src/common/fp/op/FPRecipStepFused.cpp
index da849c0a..2cb09c06 100644
--- a/src/common/fp/op/FPRecipStepFused.cpp
+++ b/src/common/fp/op/FPRecipStepFused.cpp
@@ -33,7 +33,8 @@ FPT FPRecipStepFused(FPT op1, FPT op2, FPCR fpcr, FPSR& fpsr) {
     const bool zero2 = type2 == FPType::Zero;
 
     if ((inf1 && zero2) || (zero1 && inf2)) {
-        return FPInfo<FPT>::Two(false);
+        // return +2.0
+        return FPValue<FPT, false, 0, 2>();
     }
 
     if (inf1 || inf2) {