LONG Function

Converts an expression to longword integer data type.

Extracts data from an expression and places it in a longword integer scalar or array.

result = LONG(expr)

This form is used to convert data.

result = LONG(expr, offset, [dim₁, ... , dim_n ])

This form is used to extract data.

To convert data:

expr The expression to be converted.

To extract data:

expr The expression from which to extract data.

offset The offset, in bytes, from the beginning of expr to where the extraction is to begin.

dim_i (optional) The dimensions of the result. The dimensions may be any scalar expression with up to eight dimensions specified.

For data conversion:

result A copy of expr converted to longword integer data type.

For data extraction:

result If offset is used, LONG does not convert result, but allows fields of data extracted from expr to be treated as longword integer data. If no dimensions are specified, the result is scalar.

None.

Conversion usage:

If the values of expr are not within the range of a long integer, a misleading result occurs and a message may be displayed.

For example, suppose A = 2.0 ^ 31 + 2. The following commands,

B = LONG(A) 
C = LONG(-A)

produce the erroneous results of

B = 2147483647
C = -2147483648

In addition, PV-WAVE does not check for overflow during conversion to longword integer data type.

In this example, LONG is used in two ways. First, LONG is used to convert a single-precision, floating-point array to type longword. Next, LONG is used to extract a subarray from the longword array created in the first step.

a = FINDGEN(6) + 0.5

; Create a single-precision, floating-point vector of length 6. Each 
; element has a value equal to its one-dimensional subscript plus 0.5.

PRINT, a

0.500000 1.50000 2.50000 3.50000 4.50000
5.50000

b = LONG(a)

; Convert a to type longword.

INFO, b

VARIABLE          LONG           = Array(6)

; Note that the floating-point numbers in a were truncated 
; by LONG.

PRINT, b

0       1       2       3       4       5

; Extract the last four elements of b, and place them in a.

c = LONG(b, 8, 2, 2)

; Specify a 2-by-2 long array.

INFO, c

VARIABLE          LONG           = Array(2, 2)

PRINT, c

2                3
4                5

BYTE, COMPLEX, DOUBLE, FIX, FLOAT, LINDGEN, LONARR

For more information on using this function to extract data, see the PV-WAVE Programmer's Guide.