From 097f6a83da1f93a6680ab6276ad2a21a9bbd18cf Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Tue, 20 Dec 2016 22:06:14 +0000
Subject: [PATCH] emit_x64: Document
 ExtractAndDuplicateMostSignificantBitFromPackedWords

---
 src/backend_x64/emit_x64.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/backend_x64/emit_x64.cpp b/src/backend_x64/emit_x64.cpp
index 8ffd57e9..fcba85b0 100644
--- a/src/backend_x64/emit_x64.cpp
+++ b/src/backend_x64/emit_x64.cpp
@@ -1369,6 +1369,14 @@ static void ExtractMostSignificantBitFromPackedBytes(const Xbyak::util::Cpu& cpu
     }
 }
 
+/**
+ * Extracts the most significant bits from each of the packed words, duplicates them, and packs them together.
+ *
+ *     value before:    a---------------b---------------
+ *     value after:     0000000000000000000000000000aabb
+ *
+ * @param value The register containing the value to operate on. Result will be stored in the same register.
+ */
 static void ExtractAndDuplicateMostSignificantBitFromPackedWords(BlockOfCode* code, Xbyak::Reg32 value) {
     code->and_(value, 0x80008000);
     code->shr(value, 1);