speed up flatten_fraction

Author: shashi

src/polyform.jl

@@ -257,12 +257,9 @@ function simplify_div(d::Div)
     end
 end
 
-function add_divs(x, y)
-    x_num, x_den = polyform_factors(x, get_pvar2sym(), get_sym2term())
-    y_num, y_den = polyform_factors(y, get_pvar2sym(), get_sym2term())
-
-    (_mul(x_num, y_den) + _mul(x_den, y_num)) / (_mul(x_den, y_den))
-end
+add_divs(x::Div, y::Div) = (x.num * y.den + y.num * x.den) / (x.den * y.den)
+add_divs(x::Div, y) = (x.num + y * x.den) / x.den
+add_divs(x, y::Div) = (x * y.den + y.num) / y.den
 
 """
     simplify_fractions(x)
@@ -283,6 +280,17 @@ function simplify_fractions(x)
     Fixpoint(Postwalk(RestartedChain(rules)))(x)
 end
 
+function add_with_div(x)
+    (!istree(x) || operation(x) != (+)) && return nothing
+    aa = unsorted_arguments(x)
+    !any(a->a isa Div, aa) && return nothing # no rewrite necessary
+
+    divs = filter(a->a isa Div, aa)
+    nondivs = filter(a->!(a isa Div), aa)
+    nds = isempty(nondivs) ? 0 : +(nondivs...)
+
+    return quick_cancel(add_divs(reduce(quick_cancel∘add_divs, divs), nds))
+end
 """
     flatten_fractions(x)
 
@@ -294,17 +302,15 @@ julia> flatten_fractions((1+(1+1/a)/a)/a)
 ```
 """
 function flatten_fractions(x)
-    rules = [@acrule ~a::(x->x isa Div) + ~b => add_divs(~a,~b)
-             @rule *(~~x, ~a / ~b, ~~y) / ~c => *((~~x)..., ~a, (~~y)...) / (~b * ~c)
-             @rule ~c / *(~~x, ~a / ~b, ~~y)  => (~b * ~c) / *((~~x)..., ~a, (~~y)...)]
-    Fixpoint(Postwalk(Chain(rules)))(x)
+    Fixpoint(Postwalk(PassThrough(add_with_div)))(x)
 end
 
 function fraction_iszero(x)
     !istree(x) && return _iszero(x)
+    ff = flatten_fractions(x)
     # fast path and then slow path
-    any(_iszero, numerators(flatten_fractions(x))) ||
-    any(_iszero∘expand, numerators(flatten_fractions(x)))
+    any(_iszero, numerators(ff)) ||
+    any(_iszero∘expand, numerators(ff))
 end
 
 function fraction_isone(x)

src/rewriters.jl

@@ -29,7 +29,7 @@ rewriters.
 
 """
 module Rewriters
-using SymbolicUtils: @timer
+using SymbolicUtils: @timer, unsorted_arguments
 using TermInterface: is_operation, istree, operation, similarterm, arguments, node_count
 
 export Empty, IfElse, If, Chain, RestartedChain, Fixpoint, Postwalk, Prewalk, PassThrough
@@ -159,7 +159,7 @@ function (p::Walk{ord, C, F, false})(x) where {ord, C, F}
             x = p.rw(x)
         end
         if istree(x)
-            x = p.similarterm(x, operation(x), map(PassThrough(p), arguments(x)))
+            x = p.similarterm(x, operation(x), map(PassThrough(p), unsorted_arguments(x)))
         end
         return ord === :post ? p.rw(x) : x
     else

src/rule.jl

@@ -356,7 +356,7 @@ function (acr::ACRule)(term)
         end
 
         T = symtype(term)
-        args = arguments(term)
+        args = unsorted_arguments(term)
 
         itr = acr.sets(eachindex(args), acr.arity)