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