NAG Library Function Document

nag_quicksort (m01csc)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:    $\mathbf{vec}\left[\mathbf{n}\right]$ – Pointer Input/Output

On entry: the array of objects to be sorted.

On exit: the objects rearranged into sorted order.

2:    $\mathbf{n}$ – size_tInput

On entry: the number, $n$, of objects to be sorted.

Constraint: $0\le \mathbf{n}\le \mathrm{MAX\_LENGTH}$, where $\mathrm{MAX\_LENGTH}$ is an implementation-dependent value for the maximum size of an array.

3:    $\mathbf{size}$ – size_tInput

On entry: the size of each object to be sorted.

Constraint: $1\le \mathbf{size}\le p$, where $p$ is an implementation-dependent value for the maximum size_t size on the system, divided by n if n is positive.

4:    $\mathbf{stride}$ – ptrdiff_tInput

On entry: the increment between data items in vec to be sorted.

Note: if stride is positive, vec should point at the first data object; otherwise vec should point at the last data object.

Constraint: $\mathbf{size}\le \left|\mathbf{stride}\right|\le p$, where $p$ is an implementation-dependent value for the maximum size_t size on the system, divided by n if n is positive.

5:    $\mathbf{compare}$ – function, supplied by the userExternal Function

nag_quicksort (m01csc) compares two data objects. If its arguments are pointers to a structure, this function must allow for the offset of the data field in the structure (if it is not the first).

The function must return:

$-1$	if the first data field is less than the second,
$\phantom{-}0$	if the first data field is equal to the second,
$\phantom{-}1$	if the first data field is greater than the second.

The specification of compare is:

Integer  compare (const Nag_Pointer a, const Nag_Pointer b)

1:    $\mathbf{a}$ – const Nag_Pointer Input

On entry: the first data field.

2:    $\mathbf{b}$ – const Nag_Pointer Input

On entry: the second data field.

6:    $\mathbf{order}$ – Nag_SortOrderInput

On entry: specifies whether the array is to be sorted into ascending or descending order.

Constraint: $\mathbf{order}=\mathrm{Nag\_Ascending}$ or $\mathrm{Nag\_Descending}$.

7:    $\mathbf{fail}$ – NagError *Input/Output

The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6

Error Indicators and Warnings

NE_2_INT_ARG_LT

On entry, $\left|\mathbf{stride}\right|=〈\mathit{\text{value}}〉$ while $\mathbf{size}=〈\mathit{\text{value}}〉$. These arguments must satisfy $\left|\mathbf{stride}\right|\ge \mathbf{size}$.

NE_ALLOC_FAIL

Dynamic memory allocation failed.

NE_BAD_PARAM

On entry, argument order had an illegal value.

NE_INT_ARG_GT

On entry, $\left|\mathbf{stride}\right|=〈\mathit{\text{value}}〉$.
Constraint: $\left|\mathbf{stride}\right|\le 〈\mathit{\text{value}}〉$, an implementation-dependent size that is printed in the error message.

On entry, $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{n}\le 〈\mathit{\text{value}}〉$, an implementation-dependent size that is printed in the error message.

On entry, $\mathbf{size}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{size}\le 〈\mathit{\text{value}}〉$, an implementation-dependent size that is printed in the error message.

NE_INT_ARG_LT

On entry, $\mathbf{n}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{n}\ge 0$.

On entry, $\mathbf{size}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{size}\ge 1$.

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

Program Text (m01csce.c)

10.2

Program Data

Program Data (m01csce.d)

10.3

Program Results

Program Results (m01csce.r)