Update quadword.jl

Author: JeffreySarnoff

src/doubletriple/quadword.jl

@@ -5,3 +5,65 @@ function vec_sum(x0::T, x1::T, x2::T, x3::T) where {T}
     s0, e1 = two_sum(x0, s1)
     return s0,e1,e2,e3
 end
+
+function vsum_errbranch(x::NTuple{4,T}) where {T}
+    y = zeros(T, 4)
+    r = zeros(T, 4)
+    e = zeros(T, 4)
+    j = 1
+    e[1] = x[1]
+    for i = 1:2
+        r[i], t = two_sum(e[i], x[i+1])
+        if t !== zero(T)
+            y[j] = r[i]
+            e[i+1] = t
+            j += 1
+        else    
+            e[i+1] = r[i]
+        end    
+    end
+    y[j], y[j+1] = two_sum(e[3], x[4])
+    return y
+end
+
+function quadword(x1::T, x2::T, x3::T, x4::T) where {T}
+    a1, a2 = two_sum(x1, x2)
+    b1, b2 = two_sum(x3, x4)
+    c1, c2 = two_sum(a1, b1)
+    d1, d2 = two_sum(a2, b2)
+    e1to4 = vec_sum(c1,c2,d1,d2)
+    y = vsum_errbranch(e1to4)
+    return (y...,)
+end
+
+#=
+function vec_sum_errbranch(x0::T, x1::T, x2::T, x3::T) where {T}
+    # n = 4
+    j = zero(T)
+    e0 = x0
+    r0, et1 = two_sum(e0, x1)
+    if !iszero(e1)
+        y0 = r0
+        e1 = et1
+        j += 1
+    else
+        e1 = r0
+    end
+    r1, et2 = two_sum(e1, x2)
+    if !iszero(e2)
+        if iszero(j)
+            y0 = r1
+            y1 = zero(T)
+         else
+            y1 = r1
+         end   
+         e2 = et2
+         j += 1
+    else
+         e2 = r1
+    end
+    yj, yj+1 = two_sum(e2, e3)
+    yj+2,..y3 = zero(T)
+    return y0,y1,y2,y3
+end
+=#