Issue #7652: Integrate the decimal floating point libmpdec library to speed

up the decimal module. Performance gains of the new C implementation are
between 12x and 80x, depending on the application.

Modules/_decimal/tests/bench.py

@@ -0,0 +1,116 @@
+#!/usr/bin/env python
+
+#
+# Copyright (C) 2001-2012 Python Software Foundation. All Rights Reserved.
+# Modified and extended by Stefan Krah.
+#
+
+# Usage: ../../../python bench.py
+
+
+import time
+from math import log, ceil
+from test.support import import_fresh_module
+
+C = import_fresh_module('decimal', fresh=['_decimal'])
+P = import_fresh_module('decimal', blocked=['_decimal'])
+
+
+# Pi function from the decimal.py documentation
+def pi_float(prec):
+    """native float"""
+    lasts, t, s, n, na, d, da = 0, 3.0, 3, 1, 0, 0, 24
+    while s != lasts:
+        lasts = s
+        n, na = n+na, na+8
+        d, da = d+da, da+32
+        t = (t * n) / d
+        s += t
+    return s
+
+def pi_cdecimal(prec):
+    """cdecimal"""
+    C.getcontext().prec = prec
+    D = C.Decimal
+    lasts, t, s, n, na, d, da = D(0), D(3), D(3), D(1), D(0), D(0), D(24)
+    while s != lasts:
+        lasts = s
+        n, na = n+na, na+8
+        d, da = d+da, da+32
+        t = (t * n) / d
+        s += t
+    return s
+
+def pi_decimal(prec):
+    """decimal"""
+    P.getcontext().prec = prec
+    D = P.Decimal
+    lasts, t, s, n, na, d, da = D(0), D(3), D(3), D(1), D(0), D(0), D(24)
+    while s != lasts:
+        lasts = s
+        n, na = n+na, na+8
+        d, da = d+da, da+32
+        t = (t * n) / d
+        s += t
+    return s
+
+def factorial(n, m):
+    if (n > m):
+        return factorial(m, n)
+    elif m == 0:
+        return 1
+    elif n == m:
+        return n
+    else:
+        return factorial(n, (n+m)//2) * factorial((n+m)//2 + 1, m)
+
+
+print("\n# ======================================================================")
+print("#                   Calculating pi, 10000 iterations")
+print("# ======================================================================\n")
+
+for prec in [9, 19]:
+    print("\nPrecision: %d decimal digits\n" % prec)
+    for func in [pi_float, pi_cdecimal, pi_decimal]:
+        start = time.time()
+        for i in range(10000):
+            x = func(prec)
+        print("%s:" % func.__name__.replace("pi_", ""))
+        print("result: %s" % str(x))
+        print("time: %fs\n" % (time.time()-start))
+
+
+print("\n# ======================================================================")
+print("#                               Factorial")
+print("# ======================================================================\n")
+
+C.getcontext().prec = C.MAX_PREC
+
+for n in [100000, 1000000]:
+
+    print("n = %d\n" % n)
+
+    # C version of decimal
+    start_calc = time.time()
+    x = factorial(C.Decimal(n), 0)
+    end_calc = time.time()
+    start_conv = time.time()
+    sx = str(x)
+    end_conv = time.time()
+    print("cdecimal:")
+    print("calculation time: %fs" % (end_calc-start_calc))
+    print("conversion time: %fs\n" % (end_conv-start_conv))
+
+    # Python integers
+    start_calc = time.time()
+    y = factorial(n, 0)
+    end_calc = time.time()
+    start_conv = time.time()
+    sy = str(y)
+    end_conv =  time.time()
+
+    print("int:")
+    print("calculation time: %fs" % (end_calc-start_calc))
+    print("conversion time: %fs\n\n" % (end_conv-start_conv))
+
+    assert(sx == sy)