From d496f23fd897bd816927fe2089eaf5578e28f805 Mon Sep 17 00:00:00 2001
From: Andrew Martin <andrew.thaddeus@gmail.com>
Date: Fri, 3 Jan 2020 06:42:32 -0500
Subject: [PATCH] Add word8PaddedLowerHex

---
 CHANGELOG.md                          | 1 +
 src/Data/ByteArray/Builder/Bounded.hs | 7 +++++++
 test/Main.hs                          | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 31ecc0b..ba5bb20 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 * Add `runOnto`
 * Add `Data.Bytes.Chunks.length`
 * Add `wordPaddedDec2` and `wordPaddedDec9`.
+* Add `word8PaddedLowerHex`.
 
 ## 0.3.1.0 -- 2019-11-20
 
diff --git a/src/Data/ByteArray/Builder/Bounded.hs b/src/Data/ByteArray/Builder/Bounded.hs
index dfd4231..c014036 100644
--- a/src/Data/ByteArray/Builder/Bounded.hs
+++ b/src/Data/ByteArray/Builder/Bounded.hs
@@ -47,6 +47,7 @@ module Data.ByteArray.Builder.Bounded
   , word16LowerHex
   , word16UpperHex
     -- ** 8-bit
+  , word8PaddedLowerHex
   , word8PaddedUpperHex
   , word8LowerHex
   , ascii
@@ -383,6 +384,12 @@ word8LowerHex (W8# w) = word8LowerHex# w
 word8PaddedUpperHex :: Word8 -> Builder 2
 word8PaddedUpperHex (W8# w) = word8PaddedUpperHex# w
 
+-- | Requires exactly 2 bytes. Encodes a 8-bit unsigned integer as
+-- hexadecimal, zero-padding the encoding to 2 digits. This uses
+-- lowercase for the alphabetical digits.
+word8PaddedLowerHex :: Word8 -> Builder 2
+word8PaddedLowerHex (W8# w) = word8PaddedLowerHex# w
+
 -- TODO: Is it actually worth unrolling this loop. I suspect that it
 -- might not be. Benchmark this.
 word64PaddedUpperHex# :: Word# -> Builder 16
diff --git a/test/Main.hs b/test/Main.hs
index 42c0979..f39cec3 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -64,6 +64,10 @@ tests = testGroup "Tests"
         runConcat 1 (word64PaddedUpperHex w)
         ===
         pack (showWord64PaddedUpperHex w)
+    , TQC.testProperty "word16PaddedLowerHex" $ \w ->
+        runConcat 1 (word16PaddedLowerHex w)
+        ===
+        pack (showWord16PaddedLowerHex w)
     , TQC.testProperty "wordPaddedDec2" $ TQC.forAll (TQC.choose (0,99)) $ \w ->
         Bounded.run Nat.two (Bounded.wordPaddedDec2 w)
         ===
@@ -278,6 +282,9 @@ packUtf8 = Exts.fromList . ByteString.unpack . TE.encodeUtf8 . T.pack
 showWord64PaddedUpperHex :: Word64 -> String
 showWord64PaddedUpperHex = printf "%016X" 
 
+showWord16PaddedLowerHex :: Word16 -> String
+showWord16PaddedLowerHex = printf "%04x" 
+
 runConcat :: Int -> Builder -> ByteArray
 runConcat n = Chunks.concat . run n