M438: Move Bit String

Author(s): H. Grote	Library: KERNLIB
Submitter:	Submitted: 01.12.1980
Language: CDC: Fortran and Compass, IBM: Assembler	Revised:

BTMOVE moves a contiguous string of N bits from any position in memory to any other position. Bits are numbered from left to right (most significant to least significant within words) and may be across word boundaries.

Structure:

SUBROUTINE subprogram
User Entry Names: BTMOVE
External References: UCOPY (CDC only)

Usage:

    CALL BTMOVE(SOURCE,ISRC,TARGET,ITGT,N)

moves the string of N contiguous bits starting at position ISRC in word or array SOURCE to position ITGT in word or array TARGET. The other bits in TARGET are not changed, nor is SOURCE.

Notes:

Source and target strings must not overlap in storage, else the results may be unpredictable.

Examples:

IBM:
Move the highest bit (sign-bit) in word A to the lowest position of I so that it can be treated as an integer:

    REAL A
    INTEGER*4 I
    I=0
    CALL BTMOVE(A,1,I,32,1)

CDC:
Pack the five integers of array I5(5) into one word IPACK, using 12 bits per packed integer:

    DIMENSION I5(5)
    IPOS=1
    DO 1 I = 1,5
    CALL BTMOVE(I5(I),49,IPACK,IPOS,12)
  1 IPOS=IPOS+12

Move a string of 20 characters from positions 41-60 in array A to positions 7-26 in array B:

    DIMENSION A(6),B(3)
    CALL BTMOVE(A,241,B,37,120)