Extracts bit fields from character string data and converts the result to an unsigned number.

Format

F$CVUI (start-bit,number-of-bits,string)

Return Value

Arguments

start-bit

Specifies the offset of the first bit to be extracted. The low-order (rightmost) bit of a string is position number 0 for determining the offset. Specify the offset as an integer expression.

If you specify an expression with a negative value, or with a value that exceeds the number of bits in the string, DCL displays the INVRANGE error message.

number-of-bits

Specifies the length of the bit string to be extracted, which must be less than or equal to the number of bits in the string argument.

If you specify an expression with a negative value, or with a value that is invalid when added to the bit position offset, DCL displays the INVRANGE error message.

string

Specifies the character string to be edited.

Example

$ A[0,32] = %X2B
$ SHOW SYMBOL A
  A = "+..."
$ X = F$CVUI(0,4,A)
$ SHOW SYMBOL X
  X = 11   Hex = 0000000B  Octal = 00000000013
      

This example uses an arithmetic overlay to assign the hexadecimal value 2B to all 32 bits of the symbol A. The symbol A has a string value after the overlay because it was previously undefined. (If a symbol is undefined, it has a string value as a result of an arithmetic overlay. If a symbol was previously defined, it retains the same data type after the overlay.) The hexadecimal value 2B corresponds to the ASCII character "+".

Next, the F$CVUI function extracts the low-order 4 bits from the symbol A; the low-order 4 bits contain the binary representation of the hexadecimal value B. These bits are converted, as a signed value, to an integer. The converted value, 11, is assigned to the symbol X.