From adc192ac17777014d851c9b6fe390f534c104fe2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Olivier=20Ch=C3=A9ron?= <olivier.cheron@gmail.com>
Date: Sun, 25 Jun 2017 17:11:47 +0200
Subject: [PATCH] Add constAllZero

---
 Crypto/Internal/ByteArray.hs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Crypto/Internal/ByteArray.hs b/Crypto/Internal/ByteArray.hs
index 3a23152..57ab57a 100644
--- a/Crypto/Internal/ByteArray.hs
+++ b/Crypto/Internal/ByteArray.hs
@@ -7,13 +7,33 @@
 --
 -- Simple and efficient byte array types
 --
+{-# LANGUAGE BangPatterns #-}
 {-# OPTIONS_HADDOCK hide #-}
 module Crypto.Internal.ByteArray
     ( module Data.ByteArray
     , module Data.ByteArray.Mapping
     , module Data.ByteArray.Encoding
+    , constAllZero
     ) where
 
 import Data.ByteArray
 import Data.ByteArray.Mapping
 import Data.ByteArray.Encoding
+
+import Data.Bits ((.|.))
+import Data.Word (Word8)
+import Foreign.Ptr (Ptr)
+import Foreign.Storable (peekByteOff)
+
+import Crypto.Internal.Compat (unsafeDoIO)
+
+constAllZero :: ByteArrayAccess ba => ba -> Bool
+constAllZero b = unsafeDoIO $ withByteArray b $ \p -> loop p 0 0
+  where
+    loop :: Ptr b -> Int -> Word8 -> IO Bool
+    loop p i !acc
+        | i == len  = return $! acc == 0
+        | otherwise = do
+            e <- peekByteOff p i
+            loop p (i+1) (acc .|. e)
+    len = Data.ByteArray.length b