1 files changed, 28 insertions, 0 deletions
diff --git a/src/crypto/shen_ed25519_ref/ref10CommentedCombined/sqrtm1.py b/src/crypto/shen_ed25519_ref/ref10CommentedCombined/sqrtm1.py
new file mode 100644
index 000000000..9a47fbc12
--- /dev/null
+++ b/src/crypto/shen_ed25519_ref/ref10CommentedCombined/sqrtm1.py
@@ -0,0 +1,28 @@
+q = 2**255 - 19
+
+def expmod(b,e,m):
+  if e == 0: return 1
+  t = expmod(b,e/2,m)**2 % m
+  if e & 1: t = (t*b) % m
+  return t
+
+def inv(x):
+  return expmod(x,q-2,q)
+
+def radix255(x):
+  x = x % q
+  if x + x > q: x -= q
+  x = [x,0,0,0,0,0,0,0,0,0]
+  bits = [26,25,26,25,26,25,26,25,26,25]
+  for i in range(9):
+    carry = (x[i] + 2**(bits[i]-1)) / 2**bits[i]
+    x[i] -= carry * 2**bits[i]
+    x[i + 1] += carry
+  result = ""
+  for i in range(9):
+    result = result+str(x[i])+","
+  result = result+str(x[9])
+  return result
+
+I = expmod(2,(q-1)/4,q)
+print radix255(I)