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Optimize (-a)*b or a*(-b) to -(a*b), revisiting the expression.

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This obviates the need for (-a)*(-b) because it will be simplified automatically. It also enables (a+1)*b-1 to be simplified to just ~(~a*b). Still missing simplifying a*b+b to (a+1)*b, but that's more complicated.
This commit is contained in:
Sei Lisa 2015-03-03 01:46:53 +01:00
parent 22a1a2e8ba
commit 493aed6c39
1 changed files with 12 additions and 9 deletions
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21
lslopt/lslfoldconst.py
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@ -502,15 +502,18 @@ class foldconst(object):
if nt in ('*', '/'):
# Optimize (-a)*(-b) and (-a)/(-b)
if child[0]['nt'] == 'NEG' and child[1]['nt'] == 'NEG':
child[0] = child[0]['ch'][0]
child[1] = child[1]['ch'][0]
# TODO: Try to optimize -(expr*-const).
# That would yield optimal ~(~expr*blah) from (expr+1)*blah-1.
# Also it would be cute if a*b+b would be optimized to (a+1)*b,
# which is the other form common in strided lists.
# Extract signs outside
if child[0]['nt'] == 'NEG' or child[1]['nt'] == 'NEG':
a, b = 0, 1
if child[b]['nt'] == 'NEG':
a, b = 1, 0
child[a] = child[a]['ch'][0]
parent[index] = node = {'nt':'NEG', 't':node['t'], 'ch':[node]}
if 'SEF' in node['ch'][0]:
node['SEF'] = True
# Fold the new expression
self.FoldTree(parent, index)
return
# Deal with operands in any order
a, b = 0, 1