X-Git-Url: https://mattmccutchen.net/bigint/bigint.git/blobdiff_plain/0afe80d551aa9b66b574b956cf681692399fc728..c17afa550d0a00498301454195699120e2bf58c5:/BigUnsigned.hh

diff --git a/BigUnsigned.hh b/BigUnsigned.hh
index 12dc534..adf1c00 100644
--- a/BigUnsigned.hh
+++ b/BigUnsigned.hh
@@ -62,7 +62,7 @@ public:
 	BigUnsigned(         short x);
 protected:
 	// Helpers
-	template <class X> void initFromPrimitive(X x);
+	template <class X> void initFromPrimitive      (X x);
 	template <class X> void initFromSignedPrimitive(X x);
 public:
 
@@ -78,10 +78,10 @@ public:
 protected:
 	// Helpers
 	template <class X> X convertToSignedPrimitive() const;
-	template <class X> X convertToPrimitive() const;
+	template <class X> X convertToPrimitive      () const;
 public:
 
-	// ACCESSORS
+	// BIT/BLOCK ACCESSORS
 
 	// Expose these from NumberlikeArray directly.
 	NumberlikeArray<Blk>::getCapacity;
@@ -90,10 +90,25 @@ public:
 	/* Returns the requested block, or 0 if it is beyond the length (as if
 	 * the number had 0s infinitely to the left). */
 	Blk getBlock(Index i) const { return i >= len ? 0 : blk[i]; }
+	/* Sets the requested block.  The number grows or shrinks as necessary. */
+	void setBlock(Index i, Blk newBlock);
 
 	// The number is zero if and only if the canonical length is zero.
 	bool isZero() const { return NumberlikeArray<Blk>::isEmpty(); }
 
+	/* Returns the length of the number in bits, i.e., zero if the number
+	 * is zero and otherwise one more than the largest value of bi for
+	 * which getBit(bi) returns true. */
+	Index bitLength() const;
+	/* Get the state of bit bi, which has value 2^bi.  Bits beyond the
+	 * number's length are considered to be 0. */
+	bool getBit(Index bi) const {
+		return (getBlock(bi / N) & (Blk(1) << (bi % N))) != 0;
+	}
+	/* Sets the state of bit bi to newBit.  The number grows or shrinks as
+	 * necessary. */
+	void setBit(Index bi, bool newBit);
+
 	// COMPARISONS
 
 	// Compares this to x like Perl's <=>
@@ -324,4 +339,80 @@ inline void BigUnsigned::operator >>=(int b) {
 	bitShiftRight(*this, b);
 }
 
+/* Templates for conversions of BigUnsigned to and from primitive integers.
+ * BigInteger.cc needs to instantiate convertToPrimitive, and the uses in
+ * BigUnsigned.cc didn't do the trick; I think g++ inlined convertToPrimitive
+ * instead of generating linkable instantiations.  So for consistency, I put
+ * all the templates here. */
+
+// CONSTRUCTION FROM PRIMITIVE INTEGERS
+
+/* Initialize this BigUnsigned from the given primitive integer.  The same
+ * pattern works for all primitive integer types, so I put it into a template to
+ * reduce code duplication.  (Don't worry: this is protected and we instantiate
+ * it only with primitive integer types.)  Type X could be signed, but x is
+ * known to be nonnegative. */
+template <class X>
+void BigUnsigned::initFromPrimitive(X x) {
+	if (x == 0)
+		; // NumberlikeArray already initialized us to zero.
+	else {
+		// Create a single block.  blk is NULL; no need to delete it.
+		cap = 1;
+		blk = new Blk[1];
+		len = 1;
+		blk[0] = Blk(x);
+	}
+}
+
+/* Ditto, but first check that x is nonnegative.  I could have put the check in
+ * initFromPrimitive and let the compiler optimize it out for unsigned-type
+ * instantiations, but I wanted to avoid the warning stupidly issued by g++ for
+ * a condition that is constant in *any* instantiation, even if not in all. */
+template <class X>
+void BigUnsigned::initFromSignedPrimitive(X x) {
+	if (x < 0)
+		throw "BigUnsigned constructor: "
+			"Cannot construct a BigUnsigned from a negative number";
+	else
+		initFromPrimitive(x);
+}
+
+// CONVERSION TO PRIMITIVE INTEGERS
+
+/* Template with the same idea as initFromPrimitive.  This might be slightly
+ * slower than the previous version with the masks, but it's much shorter and
+ * clearer, which is the library's stated goal. */
+template <class X>
+X BigUnsigned::convertToPrimitive() const {
+	if (len == 0)
+		// The number is zero; return zero.
+		return 0;
+	else if (len == 1) {
+		// The single block might fit in an X.  Try the conversion.
+		X x = X(blk[0]);
+		// Make sure the result accurately represents the block.
+		if (Blk(x) == blk[0])
+			// Successful conversion.
+			return x;
+		// Otherwise fall through.
+	}
+	throw "BigUnsigned::to<Primitive>: "
+		"Value is too big to fit in the requested type";
+}
+
+/* Wrap the above in an x >= 0 test to make sure we got a nonnegative result,
+ * not a negative one that happened to convert back into the correct nonnegative
+ * one.  (E.g., catch incorrect conversion of 2^31 to the long -2^31.)  Again,
+ * separated to avoid a g++ warning. */
+template <class X>
+X BigUnsigned::convertToSignedPrimitive() const {
+	X x = convertToPrimitive<X>();
+	if (x >= 0)
+		return x;
+	else
+		throw "BigUnsigned::to(Primitive): "
+			"Value is too big to fit in the requested type";
+}
+
 #endif