VMS Help Lexicals, F$CVSI  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Converts the specified bits in the specified character string to
    a signed number.

    Format

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

1 - Return Value

    The integer equivalent of the extracted bit field, converted as a
    signed value.

2 - 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, then 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.

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

 string

    Specifies the string from which the bits are taken. Specify the
    string as a character string expression.

3 - Examples

    1.$ A[0,32] = %X2B
      $ SHOW SYMBOL A
        A = "+..."
      $ X = F$CVSI(0,4,A)
      $ SHOW SYMBOL X
        X = -5   Hex = FFFFFFFB  Octal = 37777777773

      This example uses an arithmetic overlay to assign the
      hexadecimal value 2B to all 32 bits of the symbol A. For more
      information on arithmetic overlays, see the description of the
      assignment statement (=).

      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
      value of the plus sign (+).

      Next, the F$CVSI 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, -5, is assigned to the symbol X.

    2.$ SYM[0,32] = %X2A
      $ SHOW SYMBOL SYM
        SYM = "*..."
      $ Y = F$CVSI(0,33,SYM)
      %DCL-W-INVRANGE, field specification is out of bounds -
         check sign and size
      $ SHOW SYMBOL Y
      %DCL-W-UNDSYM, undefined symbol - check spelling

      In this example, the width argument specified with the F$CVSI
      function is too large. Therefore, DCL issues an error message
      and the symbol Y is not assigned a value.