From 28b368d92afe3d0bc48816209d2f42817e9bb479 Mon Sep 17 00:00:00 2001
From: Balazs Komuves <bkomuves@gmail.com>
Date: Sat, 15 Mar 2025 13:53:11 +0100
Subject: [PATCH] BN254 mini-lib (using constantine under the hood)

---
 nim/circom_witnessgen.nimble    |  4 +-
 nim/circom_witnessgen/field.nim | 77 +++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 nim/circom_witnessgen/field.nim

diff --git a/nim/circom_witnessgen.nimble b/nim/circom_witnessgen.nimble
index f88ea23..678b99e 100644
--- a/nim/circom_witnessgen.nimble
+++ b/nim/circom_witnessgen.nimble
@@ -1,6 +1,8 @@
 version     = "0.0.1"
 author      = "Balazs Komuves"
 description = "Witness generation for circom circuits"
-license     = "MIT"
+license     = "MIT OR Apache-2.0"
 
 bin = @["main"]
+
+requires "constantine >= 0.2.0"
\ No newline at end of file
diff --git a/nim/circom_witnessgen/field.nim b/nim/circom_witnessgen/field.nim
new file mode 100644
index 0000000..2e10f9e
--- /dev/null
+++ b/nim/circom_witnessgen/field.nim
@@ -0,0 +1,77 @@
+
+import pkg/constantine/math/arithmetic
+import pkg/constantine/math/io/io_bigints
+import pkg/constantine/math/io/io_fields
+import pkg/constantine/named/properties_fields
+
+#-------------------------------------------------------------------------------
+
+type 
+  B* = BigInt[254]
+  F* = Fr[BN254Snarks]
+
+const zeroF* : F  = fromHex( Fr[BN254Snarks], "0x00" )
+const oneF*  : F  = fromHex( Fr[BN254Snarks], "0x01" )
+
+func isZeroF*  (x: F )    : bool = bool(isZero(x))
+func isEqualF* (x, y: F ) : bool = bool(x == y)
+func `===`*    (x, y: F ) : bool = isEqualF(x,y)
+
+const fieldMask*     : B = fromHex( BigInt[254] , "0x3fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", bigEndian )
+const fieldPrime*    : B = fromHex( BigInt[254] , "0x30644e72e131a029b85045b68181585d2833e84879b9709143e1f593f0000001", bigEndian )
+const halfPrimPlus1* : B = fromHex( BigInt[254] , "0x183227397098d014dc2822db40c0ac2e9419f4243cdcb848a1f0fac9f8000001", bigEndian )
+
+#-------------------------------------------------------------------------------
+
+func intToF*(a: int): F =
+  var y : F
+  y.fromInt(a)
+  return y
+
+func int64ToF*(a: int64): F =
+  var y : F
+  y.fromInt(a)
+  return y
+
+func boolToF*(b: bool): F = 
+  return (if b: oneF else: zeroF)
+
+func fToBool*(x: F): bool = 
+  return not (isZeroF x)
+
+func bigToF*(big: B): F = 
+  var x : F
+  x.fromBig( big )
+  return x
+
+func fToBig*(x: F): B = 
+  return x.toBig()
+
+proc decimalToB*(s: string): B =
+  var y: B
+  let ok = y.fromDecimal(s)
+  return y
+
+proc decimalToF*(s: string): F = 
+  return bigToF(decimalToB(s))
+  # var y: F
+  # let ok = y.fromDecimal(s)     # wtf nim
+  # return y
+
+func fToDecimal*(x: F): string = 
+  return toDecimal(x)
+
+#-------------------------------------------------------------------------------
+
+func negF* (y: F  ): F  =  ( var z : F = zeroF ; z -= y ; return z )
+func invF* (y: F  ): F  =  ( var z : F = y ; inv(z) ; return z )
+
+func `+`*[n](x, y: BigInt[n] ): BigInt[n] = ( var z : BigInt[n] = x ; z += y ; return z )
+func `-`*[n](x, y: BigInt[n] ): BigInt[n] = ( var z : BigInt[n] = x ; z -= y ; return z )
+
+func `+`*(x, y: F ): F  =  ( var z : F = x ; z += y ; return z )
+func `-`*(x, y: F ): F  =  ( var z : F = x ; z -= y ; return z )
+func `*`*(x, y: F ): F  =  ( var z : F = x ; z *= y ; return z )
+func `/`*(x, y: F ): F  =  ( var z : F = x ; z *= invF(y) ; return z )
+
+#-------------------------------------------------------------------------------