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dbe3d8a692
For two reasons: - to distinguish them from the marshalling functions from constantine - they do not follow the convention that something that is marshalled can be unmarshalled, because they take in 31 bytes but produce 32 bytes
35 lines
1.4 KiB
Nim
35 lines
1.4 KiB
Nim
import ./types
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import constantine/math/arithmetic
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import constantine/math/io/io_bigints
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import constantine/math/config/curves
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func fromBytes*(_: type F, bytes: openArray[byte]): F =
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## Converts bytes into a field element. The byte array is interpreted as a
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## canonical little-endian big integer. The array should be of length 31 bytes
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## or less to ensure that it fits in a field of 254 bits. The remaining
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## 6 most-significant bits are set to 0.
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assert bytes.len <= 31
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var padded: array[32, byte]
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copyMem(addr padded[0], unsafeAddr bytes[0], bytes.len)
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let bigint = B.unmarshal(padded, littleEndian)
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return F.fromBig(bigint)
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func fromBytes*(_: type seq[F], bytes: openArray[byte]): seq[F] =
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## Converts bytes into field elements. The byte array is converted 31 bytes at
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## a time with the `F.fromBytes()` function.
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const chunkLen = 31
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var elements: seq[F]
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var chunkStart = 0
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while chunkStart < bytes.len:
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let chunkEnd = min(chunkStart + 31, bytes.len)
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let element = F.fromBytes(bytes.toOpenArray(chunkStart, chunkEnd - 1))
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elements.add(element)
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chunkStart += chunkLen
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return elements
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func toBytes*(element: F): array[32, byte] =
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## Converts a field element into its canonical representation in little-endian
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## byte order. Uses at most 254 bits, the remaining 6 most-significant bits
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## are set to 0.
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assert marshal(result, element.toBig(), littleEndian)
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