negative constants allowed in signed_mult and signed_add

Author: timsherwood

pyrtl/corecircuits.py

@@ -167,7 +167,13 @@ def signed_add(a, b):
 
     Given a length n and length m wirevector the result of the
     signed addition is length max(n,m)+1.  The inputs are twos
-    complement sign extended to the same length before adding."""
+    complement sign extended to the same length before adding.
+    If an integer is passed to either a or b, it will be converted
+    automatically to a two's complemented constant"""
+    if isinstance(a, int):
+        a = Const(a, signed=True)
+    if isinstance(b, int):
+        b = Const(b, signed=True)
     a, b = match_bitwidth(as_wires(a), as_wires(b), signed=True)
     result_len = len(a) + 1
     ext_a = a.sign_extended(result_len)
@@ -182,7 +188,19 @@ def mult_signed(a, b):
 
 
 def signed_mult(a, b):
-    """ Return a*b where a and b are treated as signed values. """
+    """ Return a*b where a and b are treated as signed values.
+
+    :param a: a wirevector to serve as first input to multiplication
+    :param b: a wirevector to serve as second input to multiplication
+
+    If an integer is passed to either a or b, it will be converted
+    automatically to a two's complemented constant"""
+    # if an integer, convert to a two's complement constant
+    if isinstance(a, int):
+        a = Const(a, signed=True)
+    if isinstance(b, int):
+        b = Const(b, signed=True)
+    # if not a wirevector yet, use standard conversion method
     a, b = as_wires(a), as_wires(b)
     final_len = len(a) + len(b)
     # sign extend both inputs to the final target length

tests/test_signed.py

@@ -127,7 +127,7 @@ def test_basic_signed_gte(self):
         self.check_trace('o     0  0  0  0  0  1  1  1  \n')
 
 
-class TestSignedAddBasicOperations(unittest.TestCase):
+class TestSignedArithBasicOperations(unittest.TestCase):
     def setUp(self):
         pyrtl.reset_working_block()
         # test with '101' in binary, which should be
@@ -152,3 +152,38 @@ def test_basic_signed_add(self):
         self.o <<= pyrtl.signed_add(self.r, self.c)
         #                  0   1   2  3  -4  -3  -2  -1
         self.check_trace('-3  -2  -1  0  -7  -6  -5  -4')
+
+    def test_basic_signed_add(self):
+        self.o <<= pyrtl.signed_add(self.r, Const(-3, signed=True))
+        self.check_trace('-3  -2  -1  0  -7  -6  -5  -4')
+
+    def test_basic_signed_add(self):
+        self.o <<= pyrtl.signed_add(self.r, -3)
+        self.check_trace('-3  -2  -1  0  -7  -6  -5  -4')
+
+    def test_basic_signed_mult(self):
+        self.o <<= pyrtl.signed_mult(self.r, self.c)
+        #                 0   1   2  3  -4  -3  -2  -1
+        self.check_trace('0  -3  -6  7  -4  -7  6  3')
+        # the above numbers don't look like multiplication but when you sign
+        # extend the inputs, truncate to the last 4 digits and then sign extend,
+        # the output I assure that they are indeed correct. :)
+
+    def test_basic_signed_mult(self):
+        self.o <<= pyrtl.signed_mult(self.r, pyrtl.Const(-2, bitwidth=3))
+        #                 0   1   2   3  -4 -3 -2 -1
+        self.check_trace('0  -2  -4  -6  -8  6  4  2')
+        # this one is multiplies by -2 and the trend is easier to see (-4 x -3 does
+        # overflow the 4 bits though).
+
+    def test_basic_signed_mult(self):
+        self.o <<= pyrtl.signed_mult(self.r, pyrtl.Const(-2, signed=True))
+        self.check_trace('0  -2  -4  -6  -8  6  4  2')
+
+    def test_basic_signed_mult(self):
+        self.o <<= pyrtl.signed_mult(self.r, -2)
+        self.check_trace('0  -2  -4  -6  -8  6  4  2')
+
+    def test_basic_signed_mult(self):
+        self.o <<= pyrtl.signed_mult(-2, self.r)
+        self.check_trace('0  -2  -4  -6  -8  6  4  2')