Implement QofInt128.pow.

Gnucash · Dec 4, 2014 · 9e37ad2 · 9e37ad2
1 parent f5c7b11
commit 9e37ad2
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Showing 3 changed files with 44 additions and 2 deletions.
diff --git a/src/libqof/qof/qofint128.cpp b/src/libqof/qof/qofint128.cpp
@@ -173,6 +173,25 @@ QofInt128::lcm(const QofInt128& b) const noexcept
     return *this / common * b;
 }
 
+/* Knuth section 4.6.3 */
+QofInt128
+QofInt128::pow(uint b) const noexcept
+{
+    if (isZero() || (m_lo == 1 && m_hi == 0) || isNan() || isOverflow())
+        return *this;
+    if (b == 0)
+        return QofInt128 (1);
+    QofInt128 retval (1), squares = *this;
+    while (b && !retval.isOverflow())
+    {
+        if (b & 1)
+            retval *= squares;
+        squares *= squares;
+        b >>= 1;
+    }
+    return retval;
+}
+
 bool
 QofInt128::isNeg () const noexcept
 {

diff --git a/src/libqof/qof/qofint128.hpp b/src/libqof/qof/qofint128.hpp
@@ -125,9 +125,11 @@ enum // Values for m_flags
 /**
  * Computes the object raised to the parameter's power
  *
- * @return A QofInt128; it will be NaN if the parameter is negative.
+ * @param b The power to raise this to. No point in taking a QofInt128, any
+ * value greater than 128 would overflow on any value other than 1.
+ * @return A QofInt128
  */
-    QofInt128 pow (const QofInt128& b) const noexcept;
+    QofInt128 pow (uint n) const noexcept;
 
 /**
  * Computes a quotient and a remainder, passed as reference parameters.

diff --git a/src/libqof/qof/test/gtest-qofint128.cpp b/src/libqof/qof/test/gtest-qofint128.cpp
@@ -411,3 +411,24 @@ TEST(qofint128_functions, GCD)
     EXPECT_EQ (one, bigger.gcd (smallest));
     EXPECT_EQ (big, smaller.lcm (smallest));
 }
+
+TEST(qofint128_functions, pow)
+{
+
+    int64_t sarg {INT64_C(53309)};
+    int64_t barg {INT64_C(4878849681579065407)};
+    QofInt128 little (sarg);
+    QofInt128 big (barg);
+    auto minus = -little;
+
+    EXPECT_EQ (QofInt128(1), little.pow(0));
+    EXPECT_EQ (QofInt128(0), QofInt128(0).pow(123));
+    EXPECT_EQ (big * big, big.pow(2));
+    EXPECT_EQ (QofInt128(UINT64_C(66326033898754),
+                         UINT64_C(10251549987585143605)), little.pow(7));
+    EXPECT_EQ (QofInt128(UINT64_C(66326033898754),
+                         UINT64_C(10251549987585143605), QofInt128::neg),
+               minus.pow(7));
+    auto over = minus.pow(9);
+    EXPECT_TRUE(over.isOverflow());
+}