cordic: vivado is bad at inferring compact adder/subtractor logic

diff --git a/migen/genlib/cordic.py b/migen/genlib/cordic.py
index d508257e14e2c7968829156ca9b6ff9f54a60726..0b9306657f7877a0e430cde83987a41cbfc6d33a 100644 (file)
--- a/migen/genlib/cordic.py
+++ b/migen/genlib/cordic.py
@@ -285,10 +285,11 @@ class TwoQuadrantCordic(Module):
                return a, s, zmax, gain
 
        def _stage(self, xi, yi, zi, xo, yo, zo, i, ai):
+               dir = Signal()
                if self.cordic_mode == "rotate":
-                       direction = zi < 0
+                       self.comb += dir.eq(zi < 0)
                else: # vector
-                       direction = yi >= 0
+                       self.comb += dir.eq(yi >= 0)
                dx = yi>>i
                dy = xi>>i
                dz = ai
@@ -296,15 +297,11 @@ class TwoQuadrantCordic(Module):
                        dx = 0
                elif self.func_mode == "hyperbolic":
                        dx = -dx
-               stmt = If(direction,
-                                       xo.eq(xi + dx),
-                                       yo.eq(yi - dy),
-                                       zo.eq(zi + dz),
-                               ).Else(
-                                       xo.eq(xi - dx),
-                                       yo.eq(yi + dy),
-                                       zo.eq(zi - dz),
-                               )
+               stmt = [
+                               xo.eq(xi + Mux(dir, dx, -dx)),
+                               yo.eq(yi + Mux(dir, -dy, dy)),
+                               zo.eq(zi + Mux(dir, dz, -dz))
+               ]
                return stmt
 
 class Cordic(TwoQuadrantCordic):