Adding the two parameter version of log to fastmath.jl. (JuliaLang#25674

)

@fastmath log(b,x) now works. This solves issue 25027.

base/fastmath.jl

@@ -173,6 +173,7 @@ mul_fast(x::T, y::T, zs::T...) where {T<:FloatTypes} =
 
 @fastmath begin
  cmp_fast(x::T, y::T) where {T<:FloatTypes} = ifelse(x==y, 0, ifelse(x<y, -1, +1))
+ log_fast(b::T, x::T) where {T<:FloatTypes} = log_fast(x)/log_fast(b)
 end
 
 eq_fast(x::T, y::T) where {T<:FloatTypes} = eq_float_fast(x, y)
@@ -366,6 +367,7 @@ sincos_fast(v) = (sin_fast(v), cos_fast(v))
  log1p_fast(x::ComplexTypes) = log(1+x)
  log2_fast(x::T) where {T<:ComplexTypes} = log(x) / log(convert(T,2))
  log_fast(x::T) where {T<:ComplexTypes} = T(log(abs2(x))/2, angle(x))
+ log_fast(b::T, x::T) where {T<:ComplexTypes} = T(log(x)/log(b))
  sin_fast(x::ComplexTypes) = -im*sinh(im*x)
  sinh_fast(x::T) where {T<:ComplexTypes} = convert(T,1)/2*(exp(x) - exp(-x))
  sqrt_fast(x::ComplexTypes) = sqrt(abs(x)) * cis(angle(x)/2)
@@ -385,7 +387,7 @@ for f in (:acos, :acosh, :angle, :asin, :asinh, :atan, :atanh, :cbrt,
  end
 end
 
-for f in (:^, :atan2, :hypot, :max, :min, :minmax)
+for f in (:^, :atan2, :hypot, :max, :min, :minmax, :log)
  f_fast = fast_op[f]
  @eval begin
  # fall-back implementation for non-numeric types

test/fastmath.jl

@@ -122,7 +122,7 @@ end
  end
  end
  for f in (:+, :-, :*, :/, :%, :(==), :!=, :<, :<=, :>, :>=, :^,
- :atan2, :hypot, :max, :min)
+ :atan2, :hypot, :max, :min, :log)
  @eval begin
  @test @fastmath($f($half, $third)) ≈ $f($half, $third)
  @test @fastmath($f($third, $half)) ≈ $f($third, $half)
@@ -156,7 +156,7 @@ end
  @test @fastmath($f($third)) ≈ $f($third) rtol=$rtol
  end
  end
- for f in (:+, :-, :*, :/, :(==), :!=, :^)
+ for f in (:+, :-, :*, :/, :(==), :!=, :^, :log)
  @eval begin
  @test @fastmath($f($half, $third)) ≈ $f($half, $third) rtol=$rtol
  @test @fastmath($f($third, $half)) ≈ $f($third, $half) rtol=$rtol
@@ -172,7 +172,7 @@ end
  chalf = (1+1im)/CT(2)
  cthird = (1-1im)/CT(3)
 
- for f in (:+, :-, :*, :/, :(==), :!=, :^)
+ for f in (:+, :-, :*, :/, :(==), :!=, :^, :log)
  @eval begin
  @test @fastmath($f($chalf, $third)) ≈ $f($chalf, $third)
  @test @fastmath($f($half, $cthird)) ≈ $f($half, $cthird)