Add wordPaddedDec4

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Revision history for small-bytearray-builder
 
+## 0.3.4.0 -- 2020-??-??
+
+* Add `wordPaddedDec4`.
+
 ## 0.3.3.0 -- 2020-02-10
 
 * Add `word64PaddedLowerHex` and `word32PaddedLowerHex`

small-bytearray-builder.cabal

@@ -1,6 +1,6 @@
 cabal-version: 2.2
 name: small-bytearray-builder
-version: 0.3.3.0
+version: 0.3.4.0
 synopsis: Serialize to a small byte arrays
 description:
   This is similar to the builder facilities provided by

src/Data/ByteArray/Builder/Bounded.hs

@@ -61,6 +61,7 @@ module Data.ByteArray.Builder.Bounded
   , char
     -- ** Native
   , wordPaddedDec2
+  , wordPaddedDec4
   , wordPaddedDec9
     -- ** Machine-Readable
     -- *** One
@@ -648,6 +649,22 @@ wordPaddedDec2 !w = Unsafe.construct $ \arr off -> do
   writeByteArray arr (off + 1) (unsafeWordToWord8 (d2 + 48))
   pure (off + 2)
 
+-- | Encode a number less than 10000 as a decimal number, zero-padding it to
+-- two digits. For example: 0 is encoded as @0000@, 5 is encoded as @0005@,
+-- and 73 is encoded as @0073@.
+--
+-- Precondition: Argument must be less than 10000. Failure to satisfy this
+-- precondition will not result in a segfault, but the resulting bytes are
+-- undefined. The implemention uses a heuristic for division that is inaccurate
+-- for large numbers.
+wordPaddedDec4 :: Word -> Builder 4
+wordPaddedDec4 !w = Unsafe.construct $ \arr off -> do
+  putRem10
+    (putRem10 $ putRem10 $ putRem10 
+     (\_ _ _ -> pure ())
+    ) arr (off + 3) w
+  pure (off + 4)
+
 -- | Encode a number less than 1e9 as a decimal number, zero-padding it to
 -- nine digits. For example: 0 is encoded as @000000000@ and 5 is encoded as
 -- @000000005@.

test/Main.hs

@@ -77,6 +77,10 @@ tests = testGroup "Tests"
         Bounded.run Nat.two (Bounded.wordPaddedDec2 w)
         ===
         pack (zeroPadL 2 (show w))
+    , TQC.testProperty "wordPaddedDec4" $ TQC.forAll (TQC.choose (0,9999)) $ \w ->
+        Bounded.run Nat.constant (Bounded.wordPaddedDec4 w)
+        ===
+        pack (zeroPadL 4 (show w))
     , TQC.testProperty "wordPaddedDec9" $ TQC.forAll (TQC.choose (0,999999999)) $ \w ->
         Bounded.run Nat.constant (Bounded.wordPaddedDec9 w)
         ===