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icestorm
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Added heuristics to further reduce LUT equations.

This commit is contained in:
ylm 2015-10-26 05:21:52 -04:00
parent e4ed27a3ab
commit 8447080d62
1 changed files with 12 additions and 5 deletions
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17
icebox/icebox_vlog.py
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@ -810,17 +810,24 @@ for lut in luts_queue:
elif not "0" in lut_bits:
const_assigns.append([net_out, "1'b1"])
else:
def equals_1(expr):
return (expr == "1") or (expr == "1'b1")
def equals_0(expr):
return (expr == "0") or (expr == "1'b0")
def make_lut_expr(bits, sigs):
if not sigs:
return "1'b%s" % bits[0]
l_expr = make_lut_expr(bits[0:len(bits)//2], sigs[1:])
h_expr = make_lut_expr(bits[len(bits)//2:len(bits)], sigs[1:])
if h_expr == l_expr: return h_expr
if sigs[0] == "0": return l_expr
if sigs[0] == "1": return h_expr
if h_expr == "1" and l_expr == "0": return sigs[0]
if h_expr == "0" and l_expr == "1": return "!" + sigs[0]
return "%s ? %s : %s" % (sigs[0], h_expr, l_expr)
if equals_0(sigs[0]): return l_expr
if equals_1(sigs[0]): return h_expr
if equals_1(h_expr) and equals_0(l_expr): return sigs[0]
if equals_0(h_expr) and equals_1(l_expr): return "!" + sigs[0]
if h_expr == "!" + l_expr: return "(%s ^ %s)" % (sigs[0], l_expr)
if equals_0(h_expr): return "(%s & !%s)" % (sigs[0], l_expr)
if equals_0(l_expr): return "(%s & %s)" % (sigs[0], h_expr)
return "(%s ? %s : %s)" % (sigs[0], h_expr, l_expr)
lut_expr = make_lut_expr(lut_bits, [net_in3, net_in2, net_in1, net_in0])
lut_assigns.append([net_out, "/* LUT %2d %2d %2d */ %s" % (lut[0], lut[1], lut[2], lut_expr)])
max_net_len = max(max_net_len, len(net_out))