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Rewrite locateErrors in a more idiomatic Haskell style.
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@jonathanknowles
jonathanknowles committed May 16, 2019
1 parent 2355b6f commit ea30367
Showing 1 changed file with 40 additions and 33 deletions.
73 changes: 40 additions & 33 deletions lib/bech32/src/Codec/Binary/Bech32/Internal.hs
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Expand Up @@ -439,40 +439,21 @@ syndrome residue = low
where
low = residue .&. 0x1f


locateErrors :: Int -> Int -> [Int]
locateErrors residue len =
if residue == 0 then [] else
if l_s0 /= -1
&& l_s1 /= -1
&& l_s2 /= -1
&& (2 * l_s1 - l_s2 - l_s0 + 2046) `mod` 1023 == 0
then
let p1 = (l_s1 - l_s0 + 1023) `mod` 1023 in
if (p1 >= len) then [] else
let l_e1 = l_s0 + (1023 - 997) * p1 in
if (l_e1 `mod` 33 > 0) then [] else [p1]
else
let findError p1 =
let s2_s1p1 = s2 `xor` (if s1 == 0 then 0 else gf_1024_exp Arr.! ((l_s1 + p1) `mod` 1023)) in
if (s2_s1p1 == 0) then [] else
let s1_s0p1 = s1 `xor` (if s0 == 0 then 0 else gf_1024_exp Arr.! ((l_s0 + p1) `mod` 1023)) in
if (s1_s0p1 == 0) then [] else
let l_s1_s0p1 = gf_1024_log Arr.! s1_s0p1 in
let p2 = ((gf_1024_log Arr.! s2_s1p1) - l_s1_s0p1 + 1023) `mod` 1023 in
if (p2 >= len || p1 == p2) then [] else
let s1_s0p2 = s1 `xor` (if s0 == 0 then 0 else gf_1024_exp Arr.! ((l_s0 + p2) `mod` 1023)) in
if (s1_s0p2 == 0) then [] else
let inv_p1_p2 = 1023 - (gf_1024_log Arr.! (gf_1024_exp Arr.! p1)) `xor` (gf_1024_exp Arr.! p2) in
let l_e2 = l_s1_s0p1 + inv_p1_p2 + (1023 - 997) * p2 in
if (l_e2 `mod` 33 > 0) then [] else
let l_e1 = (gf_1024_log Arr.! s1_s0p2) + inv_p1_p2 + (1023 - 997) * p1 in
if (l_e1 `mod` 33 > 0) then [] else
if (p1 < p2)
then [p1, p2]
else [p2, p1] in
case filter (not . null) $ map findError [0 .. len - 1] of
[] -> []
es : _ -> es
locateErrors residue len
| residue == 0 = []
| l_s0 /= -1 &&
l_s1 /= -1 &&
l_s2 /= -1 && (2 * l_s1 - l_s2 - l_s0 + 2046) `mod` 1023 == 0 =
let p1 = (l_s1 - l_s0 + 1023) `mod` 1023 in
if (p1 >= len) then [] else
let l_e1 = l_s0 + (1023 - 997) * p1 in
if (l_e1 `mod` 33 > 0) then [] else [p1]
| otherwise =
case filter (not . null) $ map findError [0 .. len - 1] of
[] -> []
es : _ -> es
where
syn = syndrome residue
s0 = syn .&. 0x3FF
Expand All @@ -482,3 +463,29 @@ locateErrors residue len =
l_s1 = gf_1024_log Arr.! s1
l_s2 = gf_1024_log Arr.! s2

findError :: Int -> [Int]
findError p1
| s2_s1p1 == 0 = []
| s1_s0p1 == 0 = []
| p2 >= len = []
| p1 == p2 = []
| s1_s0p2 == 0 = []
| l_e2 `mod` 33 > 0 = []
| l_e1 `mod` 33 > 0 = []
| (p1 < p2) = [p1, p2]
| otherwise = [p2, p1]
where
inv_p1_p2 = 1023 -
(gf_1024_log Arr.! (gf_1024_exp Arr.! p1)) `xor`
(gf_1024_exp Arr.! p2)
l_e1 = (gf_1024_log Arr.! s1_s0p2) + inv_p1_p2 + (1023 - 997) * p1
l_e2 = l_s1_s0p1 + inv_p1_p2 + (1023 - 997) * p2
l_s1_s0p1 = gf_1024_log Arr.! s1_s0p1
p2 = ((gf_1024_log Arr.! s2_s1p1) - l_s1_s0p1 + 1023) `mod` 1023
s1_s0p1 = s1 `xor`
(if s0 == 0 then 0 else gf_1024_exp Arr.! ((l_s0 + p1) `mod` 1023))
s1_s0p2 = s1 `xor`
(if s0 == 0 then 0 else gf_1024_exp Arr.! ((l_s0 + p2) `mod` 1023))
s2_s1p1 = s2 `xor`
(if s1 == 0 then 0 else gf_1024_exp Arr.! ((l_s1 + p1) `mod` 1023))

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