ROUND

ROUND returns the value of x rounded at a digit specified by n. The result has the mode, base, and scale of x.


>>-ROUND(x,n)--------------------------------------------------><

x: Real expression. If x is negative, the absolute value is rounded and the sign is restored.
n: Optionally-signed integer. It specifies the digit at which rounding is to occur.

ROUND of FIXED

The precision of a FIXED result is:

  (max(1,min(p-q+1+n,N)),n)

Where (p,q) is the precision of x, and N is the maximum number of digits allowed. Hence, n specifies the scaling factor of the result.

n must conform to the limits of scaling-factors for FIXED data. If n is greater than 0, rounding occurs at the (n)th digit to the right of the point. If n is zero or negative, rounding occurs at the (1-n)th digit to the left of the point.

The value of the result is given by the following formula, where b = 2 if x is BINARY and b = 10 if x is DECIMAL:

round(x,n) = sign(x)*(b^-n)* floor(abs(x)* (bⁿ) + 1/2)

So, in the following example, the value 6.67 is output:

    dcl X fixed dec(5,4) init(6.6666);

    put skip list( round(X,2) );

ROUND of IEEE decimal floating point

The precision of an IEEE DECIMAL FLOAT result is the same as that of the source argument.

The value of the result is given by the following formula, where where b = 10 (=radix(x)) and e = exponent(x):

round(x,n) = sign(x)*(b^(e-n))* floor(abs(x)* (b^(n-e)) + 1/2)

So, if the FLOAT(DFP) compiler option is in effect, these successive roundings of 3.1415926d0 would produce the following values:

    dcl x float dec(16) init( 3.1415926d0 );

    display( round(x,1) );  /* 3.000000000000000E+0000 */
    display( round(x,2) );  /* 3.100000000000000E+0000 */
    display( round(x,3) );  /* 3.140000000000000E+0000 */
    display( round(x,4) );  /* 3.142000000000000E+0000 */
    display( round(x,5) );  /* 3.141600000000000E+0000 */
    display( round(x,6) );  /* 3.141590000000000E+0000 */

ROUND of IEEE binary floating point

The precision of an IEEE binary floating point result is the same as that of the source argument.

Under the compiler option USAGE(ROUND(IBM)), the value of the result is the same as the source except on z/OS where if the source is not zero, then the result is obtained by turning on the rightmost bit in the source.

Under the compiler option USAGE(ROUND(ANS)), the value of the result is given by the following formula, where where b = 2 (=radix(x)) and e = exponent(x):

round(x,n) = sign(x)*(b^(e-n))* floor(abs(x)* (b^(n-e)) + 1/2)

Note that under USAGE(ROUND(ANS)), the rounding is a base 2 rounding, and the results may not be what a naive user expects. For example, if compiled with USAGE(ROUND(ANS)) and IEEE binary floating point instructions are used, these successive roundings of 3.1415926d0 would produce the following values:

    dcl x float bin(53) init( 3.1415926d0 );

    display( round(x,1) );  /* 4.000000000000000E+0000 */
    display( round(x,2) );  /* 3.000000000000000E+0000 */
    display( round(x,3) );  /* 3.000000000000000E+0000 */
    display( round(x,4) );  /* 3.250000000000000E+0000 */
    display( round(x,5) );  /* 3.125000000000000E+0000 */
    display( round(x,6) );  /* 3.125000000000000E+0000 */
    display( round(x,7) );  /* 3.156250000000000E+0000 */

ROUND of IBM hexadecimal floating point

The precision of an IBM hexadecimal floating point result is the same as that of the source argument.

Under the compiler option USAGE(ROUND(ANS)), the value of the result is given by the following formula, where where b = 16 (=radix(x)) and e = exponent(x):

round(x,n) = sign(x)*(b^(e-n))* floor(abs(x)* (b^(n-e)) + 1/2)

Note that under USAGE(ROUND(ANS)), the rounding is a base 16 rounding, and the results may not be what a naive user expects. For example, if compiled with USAGE(ROUND(ANS)) and IBM hexadecimal floating point instructions are used, these successive roundings of 3.1415926d0 would produce the following values:

    dcl x float bin(53) init( 3.1415926d0 );

    display( round(x,1) );  /*  3.000000000000000E+00  */
    display( round(x,2) );  /*  3.125000000000000E+00  */
    display( round(x,3) );  /*  3.140625000000000E+00  */
    display( round(x,4) );  /*  3.141601562500000E+00  */
    display( round(x,5) );  /*  3.141586303710938E+00  */
    display( round(x,6) );  /*  3.141592979431152E+00  */

Published: 23 December 2018