WIP: bug fixes for add/sub, not quite there yet

stillwater-sc · Dec 20, 2023 · 90e2557 · 90e2557
1 parent b2021d5
commit 90e2557
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Showing 2 changed files with 35 additions and 4 deletions.
diff --git a/include/universal/number/posit/specialized/posit_16_2.hpp b/include/universal/number/posit/specialized/posit_16_2.hpp
@@ -190,7 +190,7 @@ class posit<NBITS_IS_16, ES_IS_2> {
 			lhs_fraction += rhs_fraction;
 			// std::cout << "lhs frac : " << to_binary(lhs_fraction, 32) << '\n';
 
-			bool rcarry = 0x8000 & lhs_fraction; // first left bit
+			bool rcarry = (0x8000'0000 & lhs_fraction) != 0; // first left bit
 			if (rcarry) {
 				++exp;
 				if (exp > 3) {
@@ -245,7 +245,7 @@ class posit<NBITS_IS_16, ES_IS_2> {
 		decode_regime(lhs, m, remaining);
 
 		// extract the exponent
-		uint16_t exp = remaining >> 14;
+		uint16_t exp = remaining >> 13;
 
 		uint32_t lhs_fraction = (0x4000 | remaining) << 16;
 		int8_t shiftRight = m;
@@ -255,7 +255,7 @@ class posit<NBITS_IS_16, ES_IS_2> {
 		uint32_t rhs_fraction = (0x4000 | remaining) << 16;
 
 		// align the fractions for subtraction
-		shiftRight = (shiftRight << 1) + exp - (remaining >> 14);
+		shiftRight = (shiftRight << 2) + exp - (remaining >> 13);
 		if (shiftRight != 0) {
 			if (shiftRight >= 29) {
 				_bits = lhs;
@@ -275,7 +275,7 @@ class posit<NBITS_IS_16, ES_IS_2> {
 			--m;
 			lhs_fraction <<= 2;
 		}
-		bool ecarry = bool(0x40000000 & lhs_fraction);
+		bool ecarry = (0x4000'0000 & lhs_fraction) != 0;
 		if (!ecarry) {
 			if (exp == 0) --m;
 			exp ^= 1;

diff --git a/static/posit/specialized/posit_16_2.cpp b/static/posit/specialized/posit_16_2.cpp
@@ -79,6 +79,37 @@ try {
 	float fa, fb;
 	posit<16, 1> a, b, c;
 
+	{
+		posit<16, 2> a, b, c, cref;
+		float fa, fb, fc;
+		/*
+		FAIL
+		1.3877787807814456755e-17 +             -3.9990234375 !=            -1.99951171875 golden reference is             -3.9990234375
+			0b0.000000000000001.. +     0b1.10.01.11111111111 !=     0b1.10.00.11111111111 golden reference is     0b1.10.01.11111111111
+		 */
+		a.setbits(0x0001);
+		b.setbits(0xCFFF);  // 0b1.10.0'1.111'1111'1111
+		c = a + b;
+		fa = float(a);
+		fb = float(b);
+		fc = fa + fb;
+		cref = fc;
+		std::cout 
+			<< std::setw(NUMBER_COLUMN_WIDTH) << a << " + "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << b << " = "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << c << '\n';
+		std::cout
+			<< std::setw(NUMBER_COLUMN_WIDTH) << fa << " + "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << fb << " = "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << fc << '\n';
+		std::cout
+			<< std::setw(NUMBER_COLUMN_WIDTH) << to_binary(fa) << " + "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << to_binary(fb) << " = "
+			<< std::setw(NUMBER_COLUMN_WIDTH) << to_binary(fc) << '\n';
+		ReportBinaryOperation(a, "+", b, c);
+		ReportBinaryArithmeticError("bla", "+", a, b, c, cref);
+	}
+
 	nrOfFailedTestCases += ReportTestResult(VerifyAddition         <nbits, es>(reportTestCases), tag, "add            (native)  ");
 	return 0;
 /*