In the 32-bit build, dec_hash() raised InvalidOperation if the operand

had a coefficient with MAX_PREC=425000000 digits and a negative exponent.
Increasing the context limits above the official values fixes the issue
and is safe (in this case!).

1 files changed, 45 insertions, 0 deletions

diff --git a/Modules/_decimal/tests/bignum.py b/Modules/_decimal/tests/bignum.py
new file mode 100644
index 0000000000..9e9e769b65
--- /dev/null
+++ b/Modules/_decimal/tests/bignum.py
@@ -0,0 +1,45 @@
+#
+# These tests require gmpy and test the limits of the 32-bit build. The
+# limits of the 64-bit build are so large that they cannot be tested
+# on accessible hardware.
+#
+
+import sys
+from decimal import *
+from gmpy import mpz
+
+
+_PyHASH_MODULUS = sys.hash_info.modulus
+# hash values to use for positive and negative infinities, and nans
+_PyHASH_INF = sys.hash_info.inf
+_PyHASH_NAN = sys.hash_info.nan
+
+# _PyHASH_10INV is the inverse of 10 modulo the prime _PyHASH_MODULUS
+_PyHASH_10INV = pow(10, _PyHASH_MODULUS - 2, _PyHASH_MODULUS)
+
+def xhash(coeff, exp):
+    sign = 1
+    if coeff < 0:
+        sign = -1
+        coeff = -coeff
+    if exp >= 0:
+        exp_hash = pow(10, exp, _PyHASH_MODULUS)
+    else:
+        exp_hash = pow(_PyHASH_10INV, -exp, _PyHASH_MODULUS)
+    hash_ = coeff * exp_hash % _PyHASH_MODULUS
+    ans = hash_ if sign == 1 else -hash_
+    return -2 if ans == -1 else ans
+
+
+x = mpz(10) ** 425000000 - 1
+coeff = int(x)
+
+d = Decimal('9' * 425000000 + 'e-849999999')
+
+h1 = xhash(coeff, -849999999)
+h2 = hash(d)
+
+assert h2 == h1
+
+
+