COMPUTE (ABAP Keyword) introduction & details

COMPUTE

Basic

form

COMPUTE n = arithexp.

Effect

Evaluates the arithmetic

expression arithexp and places the result in the field n .

Allows use of

the four basic calculation types + , – , * and / , the whole number division

operators DIV (quotient) and MOD (remainder), the exponentiation operator **

(exponentiation ” X ** Y means X to the power of Y ) as well as the functions

listed below.

When evaluating mixed expressions, functions have priority.

Then comes exponentiation, followoed by the “point operations” * , / , DIV and

MOD , and finally + and – . Any combination of parentheses is also

allowed.

The fields involved are usually of type I , F or P , but there

are exceptions to this rule (see below).

You can omit the key word

COMPUTE .

Built-in functions

Functions for all number types

ABS

Amount (absolute value) |x| of x SIGN Sign (preceding sign) of x;

1 x

> 0

SIGN( x ) = 0 if x = 0

-1 x < pi ="

3.1415926535897932)" e =" 2.7182818284590452"> 0 SQRT Square root of a

non-negative number

String functions

STRLEN Length of a string up

to the last non-blank character (i.e. the occupied length )

Function

expressions consist of three parts:

Function identifier directly followed by

an opening parenthesis Argument Closing parenthesis

All parts of an

expression, particularly any parts of a function expression, must be separated

from each other by at least one blank.

Example

The following

statements, especially the arithmetic expressions, are syntactically

correct:

DATA: I1 TYPE I, I2 TYPE I, I3 TYPE I,

F1 TYPE F, F2 TYPE

F,

WORD1(10), WORD2(20).

…

F1 = ( I1 + EXP( F2 ) ) * I2 / SIN( 3 – I3

).

COMPUTE F1 = SQRT( SQRT( ( I1 + I2 ) * I3 ) + F2 ).

I1 = STRLEN( WORD1

) + STRLEN( WORD2 ).

Notes

When used in calculations, the

amount of CPU time needed depends on the data type. In very simple terms, type I

is the cheapest, type F needs longer and type P is the most

expensive.

Normally, packed numbers arithmetic is used to evaluate arithmetic

expressions. If, however, the expression contains a floating point function, or

there is at least one type F operand, or the result field is type F , floating

point arithmetic is used instead for the entire expression. On the other hand,

if only type I fields or date and time fields occur (see below), the calculation

involves integer operations.

You can also perform calculations on numeric

fields other than type I , F or P . Before executing calculations, the necessary

type conversions are performed (see MOVE ). You can, for instance, subtract one

date field (type D ) from another, in order to calculate the number of days

difference. However, for reasons of efficiency, only operands of the same number

type should be used in one arithmetic expression (apart from the operands of

STRLEN ). This means that no conversion is necessary and special optimization

procedures can be performed.

Division by 0 results in termination unless the

dividend is also 0 ( 0 / 0 ). In this case, the result is 0.

As a string

processing command, the STRLEN operator treats operands (regardless of type) as

character strings, without triggering internal conversions. On the other hand,

the operands of floating point functions are converted to type F if they have

another type.

Example

Date and time arithmetic

DATA: DAYS

TYPE I,

DATE_FROM TYPE D VALUE ’19911224′,

DATE_TO TYPE D VALUE

’19920101′,

DAYS = DATE_TO – DATE_FROM.

DAYS now contains the

value 8.

DATA: SECONDS TYPE I,

TIME_FROM TYPE T VALUE

’200000′,

TIME_TO TYPE T VALUE ’020000′.

SECONDS = ( TIME_TO – TIME_FROM )

MOD 86400.

SECONDS now contains the value 21600 (i.e. 6 hours). The

operation ” MOD 86400 ” ensures that the result is always a positive number,

even if the period extends beyond midnight.

Note

Packed numbers

arithmetic:

All P fields are treated as whole numbers. Calculations

involving decimal places require additional programming to include

multiplication or division by 10, 100, … . The DECIMALS specification with the

DATA declaration is effective only for output with WRITE .

If, however, fixed

point arithmetic is active, the DECIMALS specification is also taken into

account. In this case, intermediate results are calculated with maximum accuracy

(31 decimal places). This applies particularly to division.

For this reason,

you should always set the program attribute “Fixed point

arithmetic”.

Example

DATA P TYPE P.

P = 1 / 3 *

3.

Without “fixed point arithmetic”, P has the value 0, since ” 1 / 3

” is rounded down to 0.

With fixed point arithmetic, P has the value 1, since

the intermediate result of ” 1 / 3 ” is

0.333333333333333333333333333333.

Note

Floating point

arithmetic

With floating point arithmetic, you must always expect some

loss of accuracy through rounding errors (ABAP/4 number types

).

Note

Exponentiation

The exponential expression “x**y” means

x*x*…*x y times, provided that y is a natural number. For any value of y, x**y

is explained by exp(y*log(x)).

Operators of the same ranke are evaluated from

left to right. Only the exponential operator, as is usual in mathematics, is

evaluated from right to left . The expression ” 4 ** 3 ** 2 ” thus corresponds

to ” 4 ** ( 3 ** 2 ) ” and not ” ( 4 ** 3 ) ** 2 “, so the result is 262144 and

not 4096.

The following resrtictions apply for the expression ” X ** Y “: If

X is equal to 0, Y must be positive. If X is negative, Y must be a whole

number.

Note

DIV and MOD

The whole number division operators

DIV and MOD are defined as follows:

ndiv = n1 DIV n2

nmod = n1 MOD

n2

so that:

n1 = ndiv * n2 + nmod ndiv is a whole number 0 <= nmod

< |n2|

A runtime error occurs if n2 is equal to 0 and n1 is not equal to

0.

Example

DATA: D1 TYPE I, D2 TYPE I, D3 TYPE I, D4 TYPE I,

M1

TYPE P DECIMALS 1, M2 TYPE P DECIMALS 1,

M3 TYPE P DECIMALS 1, M4 TYPE P

DECIMALS 1,

PF1 TYPE F VALUE ‘+7.3′,

PF2 TYPE F VALUE ‘+2.4′,

NF1 TYPE

F VALUE ‘-7.3′,

NF2 TYPE F VALUE ‘-2.4′,

D1 = PF1 DIV PF2. M1 = PF1 MOD

PF2.

D2 = NF1 DIV PF2. M2 = NF1 MOD PF2.

D3 = PF1 DIV NF2. M3 = PF1 MOD

NF2.

D4 = NF1 DIV NF2. M4 = NF1 MOD NF2.

The variables now have

the following values:

D1 = 3, M1 = 0.1,

D2 = – 4, M2 = 2.3,

D3 = –

3, M3 = 0.1,

D4 = 4, M4 = 2.3.

Example

Functions ABS , SIGN , CEIL

, FLOOR , TRUNC , FRAC

DATA: I TYPE I,

P TYPE P DECIMALS 2,

M

TYPE F VALUE ‘-3.5′,

D TYPE P DECIMALS 1.

P = ABS( M ). ” 3,5

I = P. ”

4 – commercially rounded

I = M. ” -4

I = CEIL( P ). ” 4 – next largest

whole number

I = CEIL( M ). ” -3

I = FLOOR( P ). ” 3 – next smallest whole

number

I = FLOOR( M ). ” -4

I = TRUNC( P ). ” 3 – whole number part

I =

TRUNC( M ). ” -3

D = FRAC( P ). ” 0,5 – decimal part

D = FRAC( M ). ”

-0,5

Notes

Floating point functions

Although the functions

SIN , COS and TAN are defined for any numbers, the results are imprecise if the

argument is greater than about 1E8 , i.e. 10**8.

The logarithm for a base

other than e or 10 is calculated as follows:

Logarithm of b for base a =

LOG( b ) / LOG( a )

Note

Runtime errors

Depending on the

operands, the above operators and functions can cause runtime errors (e.g. when

evaluating the logarithm with a negative argument).

Related ADD , SUBTRACT ,

MULTIPLY , DIVIDE , MOVE