From d3fd03d67e1314cc87af04e3d5dd5a256306c2b2 Mon Sep 17 00:00:00 2001
From: fallenoak <git@fallenoak.me>
Date: Mon, 23 Jan 2023 22:10:24 -0600
Subject: [PATCH] feat(big): add 64-bit-centric ops

---
 storm/CMakeLists.txt |  1 +
 storm/big/Ops.cpp    | 24 ++++++++++++++++
 storm/big/Ops.hpp    | 12 ++++++++
 test/Big.cpp         | 68 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 105 insertions(+)
 create mode 100644 storm/big/Ops.cpp
 create mode 100644 storm/big/Ops.hpp
 create mode 100644 test/Big.cpp

diff --git a/storm/CMakeLists.txt b/storm/CMakeLists.txt
index 92ef8c9..c204bee 100644
--- a/storm/CMakeLists.txt
+++ b/storm/CMakeLists.txt
@@ -3,6 +3,7 @@ check_cxx_compiler_flag(-Wno-invalid-offsetof HAS_NO_INVALID_OFFSETOF)
 
 file(GLOB STORM_SOURCES
     "*.cpp"
+    "big/*.cpp"
     "hash/*.cpp"
     "queue/*.cpp"
     "string/*.cpp"
diff --git a/storm/big/Ops.cpp b/storm/big/Ops.cpp
new file mode 100644
index 0000000..d2200d4
--- /dev/null
+++ b/storm/big/Ops.cpp
@@ -0,0 +1,24 @@
+#include "storm/big/Ops.hpp"
+
+uint32_t ExtractLowPart(uint64_t& value) {
+    auto low = static_cast<uint32_t>(value);
+    value >>= 32;
+
+    return low;
+}
+
+uint32_t ExtractLowPartSx(uint64_t& value) {
+    auto low = static_cast<uint32_t>(value);
+    value >>= 32;
+
+    if (value >= 0x80000000) {
+        reinterpret_cast<uint32_t*>(&value)[0] = value;
+        reinterpret_cast<uint32_t*>(&value)[1] = -1;
+    }
+
+    return low;
+}
+
+uint64_t MakeLarge(uint32_t low, uint32_t high) {
+    return low + (static_cast<uint64_t>(high) << 32);
+}
diff --git a/storm/big/Ops.hpp b/storm/big/Ops.hpp
new file mode 100644
index 0000000..fb0b9e5
--- /dev/null
+++ b/storm/big/Ops.hpp
@@ -0,0 +1,12 @@
+#ifndef STORM_BIG_OPS_HPP
+#define STORM_BIG_OPS_HPP
+
+#include <cstdint>
+
+uint32_t ExtractLowPart(uint64_t& value);
+
+uint32_t ExtractLowPartSx(uint64_t& value);
+
+uint64_t MakeLarge(uint32_t low, uint32_t high);
+
+#endif
diff --git a/test/Big.cpp b/test/Big.cpp
new file mode 100644
index 0000000..702a5d9
--- /dev/null
+++ b/test/Big.cpp
@@ -0,0 +1,68 @@
+#include "storm/big/Ops.hpp"
+#include "test/Test.hpp"
+
+TEST_CASE("ExtractLowPart", "[big]") {
+    SECTION("extracts low part of 0") {
+        uint64_t value = 0;
+        auto low = ExtractLowPart(value);
+
+        REQUIRE(low == 0);
+        REQUIRE(value == 0);
+    }
+
+    SECTION("extracts low part of 0x12345678") {
+        uint64_t value = 0x12345678;
+        auto low = ExtractLowPart(value);
+
+        REQUIRE(low == 0x12345678);
+        REQUIRE(value == 0);
+    }
+
+    SECTION("extracts low part of 0xAAAABBBBCCCCDDDD") {
+        uint64_t value = 0xAAAABBBBCCCCDDDD;
+        auto low = ExtractLowPart(value);
+
+        REQUIRE(low == 0xCCCCDDDD);
+        REQUIRE(value == 0xAAAABBBB);
+    }
+}
+
+TEST_CASE("ExtractLowPartSx", "[big]") {
+    SECTION("extracts low part of 0") {
+        uint64_t value = 0;
+        auto low = ExtractLowPartSx(value);
+
+        REQUIRE(low == 0);
+        REQUIRE(value == 0);
+    }
+
+    SECTION("extracts low part of 0x12345678") {
+        uint64_t value = 0x12345678;
+        auto low = ExtractLowPartSx(value);
+
+        REQUIRE(low == 0x12345678);
+        REQUIRE(value == 0);
+    }
+
+    SECTION("extracts low part of 0xAAAABBBBCCCCDDDD") {
+        uint64_t value = 0xAAAABBBBCCCCDDDD;
+        auto low = ExtractLowPartSx(value);
+
+        REQUIRE(low == 0xCCCCDDDD);
+        REQUIRE(value == 0xFFFFFFFFAAAABBBB);
+    }
+}
+
+TEST_CASE("MakeLarge", "[big]") {
+    SECTION("creates uint64_t out of 0xAABBCCDD and 0x11223344") {
+        uint64_t value = MakeLarge(0xAABBCCDD, 0x11223344);
+
+        REQUIRE(value == 0x11223344AABBCCDD);
+    }
+
+    SECTION("creates uint64_t out of 0 and 0x11223344") {
+        uint64_t value = MakeLarge(0x00000000, 0x11223344);
+
+        REQUIRE(value == 0x1122334400000000);
+    }
+}