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Document conversion of bytes into field elements

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This commit is contained in:
Mark Spanbroek 2023-11-02 09:19:14 +01:00
parent 0344d9ab45
commit eb56d5bba2
1 changed files with 6 additions and 0 deletions
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6
poseidon2/io.nim
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@ -3,6 +3,10 @@ import constantine/math/arithmetic
import constantine/math/io/io_bigints
func unmarshal*(_: type F, bytes: openArray[byte]): F =
## Converts bytes into a field element. The byte array is interpreted as a
## canonical little-endian big integer. The array should be of length 31 bytes
## or less to ensure that it fits in a field of 254 bits. The remaining
## 6 most-significant bits are set to 0.
assert bytes.len <= 31
var padded: array[32, byte]
copyMem(addr padded[0], unsafeAddr bytes[0], bytes.len)
@ -10,6 +14,8 @@ func unmarshal*(_: type F, bytes: openArray[byte]): F =
return F.fromBig(bigint)
func unmarshal*(_: type seq[F], bytes: openArray[byte]): seq[F] =
## Converts bytes into field elements. The byte array is converted 31 bytes at
## a time with the `F.unmarshal()` function.
const chunkLen = 31
var elements: seq[F]
var chunkStart = 0