Add replicate

CHANGELOG.md

@@ -5,6 +5,10 @@ Note: Prior to version 0.3.4.0, this library was named
 `small-bytearray-builder` is now just a compatibility shim
 to ease the migration process.
 
+## 0.3.6.0 -- 2020-??-??
+
+* Add `replicate`.
+
 ## 0.3.5.0 -- 2020-05-01
 
 * Add `wordLEB128` and `word64LEB128`.

bytebuild.cabal

@@ -1,6 +1,6 @@
 cabal-version: 2.2
 name: bytebuild
-version: 0.3.5.0
+version: 0.3.6.0
 synopsis: Serialize to a small byte arrays
 description:
   This is similar to the builder facilities provided by

src/Data/Bytes/Builder.hs

@@ -118,10 +118,14 @@ module Data.Bytes.Builder
     -- * Encode Floating-Point Types
     -- ** Human-Readable
   , doubleDec
+    -- * Replication
+  , replicate
     -- * Control
   , flush
   ) where
 
+import Prelude hiding (replicate)
+
 import Control.Exception (SomeException,toException)
 import Control.Monad.ST (ST,runST)
 import Control.Monad.IO.Class (MonadIO,liftIO)
@@ -1130,6 +1134,17 @@ backwardsWordLoop arr off0 x0 = go off0 x0 where
       go (off + 1) y
     else pure off
 
+-- | Replicate a byte the given number of times.
+replicate ::
+     Int -- ^ Number of times to replicate the byte
+  -> Word8 -- ^ Byte to replicate
+  -> Builder
+replicate !len !w = fromEffect len
+  (\marr off -> do
+    PM.setByteArray marr off len w
+    pure (off + len)
+  )
+
 -- Based on C code from https://stackoverflow.com/a/5558614
 -- For numbers less than 1073741829, this gives a correct answer.
 approxDiv10 :: Word -> Word