Avoid ReshapedArray using Int128 in kernel (#449)

Author: tgymnich

src/device/opencl/math.jl

@@ -182,3 +182,25 @@ end
 
 
 # TODO: half and native
+
+function _mulhi(a::Int64, b::Int64)
+    shift = sizeof(a) * 4
+    mask = typemax(UInt32)
+    a1, a2 = (a >> shift), a & mask
+    b1, b2 = (b >> shift), b & mask
+    a1b1, a1b2, a2b1 = a1*b1, a1*b2, a2*b1
+    t1 = a1b2 + _mulhi(a2 % UInt32, b2 % UInt32)
+    t2 = a2b1 + (t1 & mask)
+    a1b1 + (t1 >> shift) + (t2 >> shift)
+end
+@static if isdefined(Base.MultiplicativeInverses, :_mul_high)
+    _mulhi(a::T, b::T) where {T<:Union{Signed, Unsigned}} = Base.MultiplicativeInverses._mul_high(a, b)
+    @device_override Base.MultiplicativeInverses._mul_high(a::Int64, b::Int64) = _mulhi(a, b)
+else
+    _mulhi(a::T, b::T) where {T<:Union{Signed, Unsigned}} = ((widen(a)*b) >>> (sizeof(a)*8)) % T
+    @device_override function Base.div(a::Int64, b::Base.MultiplicativeInverses.SignedMultiplicativeInverse{Int64})
+        x = _mulhi(a, b.multiplier)
+        x += (a*b.addmul) % Int64
+        ifelse(abs(b.divisor) == 1, a*b.divisor, (signbit(x) + (x >> b.shift)) % Int64)
+    end
+end