From 2b8cc51ad88e4ac4a41373d07ac12c21acf68237 Mon Sep 17 00:00:00 2001
From: fallenoak <git@fallenoak.me>
Date: Wed, 1 Feb 2023 22:12:20 -0600
Subject: [PATCH] feat(big): add InsertLowPart

---
 storm/big/Ops.cpp |  4 ++++
 storm/big/Ops.hpp |  2 ++
 test/Big.cpp      | 26 ++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/storm/big/Ops.cpp b/storm/big/Ops.cpp
index 01418a4..4409e8a 100644
--- a/storm/big/Ops.cpp
+++ b/storm/big/Ops.cpp
@@ -95,6 +95,10 @@ uint32_t HighBitPos(const BigBuffer& buffer) {
     return 0;
 }
 
+void InsertLowPart(uint64_t& value, uint32_t low) {
+    value = (value << 32) | 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
index ca8d683..3a2194e 100644
--- a/storm/big/Ops.hpp
+++ b/storm/big/Ops.hpp
@@ -21,6 +21,8 @@ void FromUnsigned(BigBuffer& buffer, uint32_t value);
 
 uint32_t HighBitPos(const BigBuffer& a);
 
+void InsertLowPart(uint64_t& value, uint32_t low);
+
 uint64_t MakeLarge(uint32_t low, uint32_t high);
 
 void Mul(BigBuffer& a, const BigBuffer& b, uint64_t c);
diff --git a/test/Big.cpp b/test/Big.cpp
index 0b5e6ba..9ebce01 100644
--- a/test/Big.cpp
+++ b/test/Big.cpp
@@ -263,6 +263,32 @@ TEST_CASE("HighBitPos", "[big]") {
     }
 }
 
+TEST_CASE("InsertLowPart", "[big]") {
+    SECTION("inserts low part 0xABCD1111 into value 0") {
+        uint64_t value = 0;
+        uint32_t low = 0xABCD1111;
+        InsertLowPart(value, low);
+
+        CHECK(value == 0xABCD1111);
+    }
+
+    SECTION("inserts low part 0xABCD1111 into value 0xCCCCCCCC") {
+        uint64_t value = 0xCCCCCCCC;
+        uint32_t low = 0xABCD1111;
+        InsertLowPart(value, low);
+
+        CHECK(value == 0xCCCCCCCCABCD1111);
+    }
+
+    SECTION("inserts low part 0x12345678 into value 0xA0B1C2D3E4F5A6B7") {
+        uint64_t value = 0xA0B1C2D3E4F5A6B7;
+        uint32_t low = 0x12345678;
+        InsertLowPart(value, low);
+
+        CHECK(value == 0xE4F5A6B712345678);
+    }
+}
+
 TEST_CASE("Mul", "[big]") {
     SECTION("multiplies 0 and 1") {
         BigData* a;