c impl: simple script to output points in similar format to py and sa…

…ge impls

src/.gitignore

@@ -11,3 +11,4 @@ psha256
 bls_hash
 hash_and_try
 *.sage.py
+__pycache__

src/test/to_affine.py

@@ -0,0 +1,68 @@
+#!/usr/bin/python
+#
+# (C) 2019 Riad S. Wahby <rsw@cs.stanford.edu>
+#
+# convert the output of the hash_to_* executables from Jacobian to affine coordinates
+
+import sys
+
+p = 0x1a0111ea397fe69a4b1ba7b6434bacd764774b84f38512bf6730d2a0f6b0f6241eabfffeb153ffffb9feffffffffaaab
+
+def invert_modp(val, prime=p):
+    if val % prime == 0:
+        return None
+    (inv, d) = ext_euclid_l(val % prime, prime)
+    if d != 1:
+        return None
+    assert (inv * val - 1) % prime == 0
+    return inv % prime
+
+def ext_euclid_l(a, b):
+    (t, t_, r, r_) = (1, 0, a, b)
+
+    while r != 0:
+        ((quot, r), r_) = (divmod(r_, r), r)
+        (t_, t) = (t, t_ - quot * t)
+
+    return (t_, r_)
+
+def invert_modp2(a, b, prime=p):
+    a2b2Inv = invert_modp(a ** 2 + b ** 2, prime)
+    return ((a * a2b2Inv) % prime, prime - (b * a2b2Inv) % prime)
+
+def mul_modp2(a, b, c, d):
+    e = (a * c - b * d) % p
+    f = (a * d + b * c) % p
+    return (e, f)
+
+def print_g1(vals):
+    (x, y, z) = vals[:3]
+    z3Inv = invert_modp(z ** 3)
+    x = (x * z3Inv * z) % p
+    y = (y * z3Inv) % p
+    print("         x =", hex(x))
+    print("         y =", hex(y))
+
+def print_g2(vals):
+    (x0, x1, y0, y1, z0, z1) = vals[:6]
+    (z20, z21) = mul_modp2(z0, z1, z0, z1)
+    (z30, z31) = mul_modp2(z0, z1, z20, z21)
+    (z3I0, z3I1) = invert_modp2(z30, z31)
+    (x0, x1) = mul_modp2(x0, x1, z3I0, z3I1)
+    (x0, x1) = mul_modp2(x0, x1, z0, z1)
+    (y0, y1) = mul_modp2(y0, y1, z3I0, z3I1)
+    print("        x0 =", hex(x0))
+    print("        x1 =", hex(x1))
+    print("        y0 =", hex(y0))
+    print("        y1 =", hex(y1))
+
+def main():
+    for line in sys.stdin.readlines():
+        vals = eval(line)   # pylint: disable=eval-used
+        if len(vals) % 2 == 1:
+            print_g1(vals)
+        else:
+            print_g2(vals)
+
+if __name__ == "__main__":
+    main()