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# vDSP_vqint

Calculates single-precision vector quadratic interpolation.

```
extern void vDSP_vqint(const float *__A, const float *__B, vDSP_Stride __IB, float *__C, vDSP_Stride __IC, vDSP_Length __N, vDSP_Length __M);
```

## Parameters

`__A`

Single-precision real input vector with a stride of 1.

`__B`

Single-precision real input vector. Integer parts are indices into `A` and fractional parts are interpolation constants

`__IB`

Stride for `B`.

`__C`

Single-precision real output vector.

`__IC`

Stride for `C`.

`__N`

Count for `C`.

`__M`

Length of `A`. Must be greater than or equal to 3.

## Discussion

Generates `C` by interpolating between neighboring values of `A` as controlled by values in `B`. The integer portion of each element in `B` is the zero-based index of the second element of a triple of adjacent values in vector `A`.

The value of the corresponding element of `C` is derived from these three values by quadratic interpolation, using the fractional part of the value in `B`. The calculation is equivalent to the following pseudocode:

```objc
for (n = 0; n < N; ++n)
{
    b = max(trunc(B[n]), 1);
    a = B[n] - b;
    C[n] = (A[b-1]*(a**2-a)
           + A[b]*(2-2*a**2)
           + A[b+1]*(a**2+a))
           / 2;
}
```

Argument `M` is not used in the calculation. However, the integer parts of the values in `B` must be less than or equal to `M` - 2.

---

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