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Fix Issue 6657 - dotProduct overload for small fixed size arrays #6990

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May 3, 2019
Merged

Fix Issue 6657 - dotProduct overload for small fixed size arrays #6990

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25 changes: 25 additions & 0 deletions std/numeric.d
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Original file line number Diff line number Diff line change
Expand Up @@ -1774,6 +1774,24 @@ dotProduct(F1, F2)(in F1[] avector, in F2[] bvector)
return sum0;
}

/// ditto
F dotProduct(F, uint N)(const ref scope F[N] a, const ref scope F[N] b)
if (N <= 16)
{
F sum0 = 0;
F sum1 = 0;
static foreach (i; 0 .. N / 2)
{
sum0 += a[i*2] * b[i*2];
sum1 += a[i*2+1] * b[i*2+1];
}
static if (N % 2 == 1)
{
sum0 += a[N-1] * b[N-1];
}
return sum0 + sum1;
}

@system unittest
{
// @system due to dotProduct and assertCTFEable
Expand All @@ -1785,6 +1803,13 @@ dotProduct(F1, F2)(in F1[] avector, in F2[] bvector)
T[] b = [ 4.0, 6.0, ];
assert(dotProduct(a, b) == 16);
assert(dotProduct([1, 3, -5], [4, -2, -1]) == 3);
// Test with fixed-length arrays.
T[2] c = [ 1.0, 2.0, ];
T[2] d = [ 4.0, 6.0, ];
assert(dotProduct(c, d) == 16);
T[3] e = [1, 3, -5];
T[3] f = [4, -2, -1];
assert(dotProduct(e, f) == 3);
}}

// Make sure the unrolled loop codepath gets tested.
Expand Down