mvbits: Move a Bit Field

The subroutine is called by:

Example: mvbits:

demo% cat mvb1.f 
* mvb1.f -- From src, initial bit 0, move 3 bits to des, initial bit 3.
*    src    des 
* 543210 543210 ¨ Bit numbers 
* 000111 000001 ¨ Values before move
* 000111 111001 ¨ Values after move
    INTEGER*4 src, ini1, nbits, des, ini2 
    data src, ini1, nbits, des, ini2 
&             / 7,    0,     3,   1,    3 / 
    call mvbits ( src, ini1, nbits, des, ini2 ) 
    write (*,"(5o3)") src, ini1, nbits, des, ini2 
    end 
demo% f77 -silent mvb1.f
demo% a.out 
  7  0  3 71  3
demo%

Note the following:

• Bits are numbered 0 to 31, from least significant to most significant.

• mvbits changes only bits ini2 through ini2+nbits-1 of the des location, and no bits of the src location.

• The restrictions are:

  • ini1 + nbits >= 32

  • ini2 + nbits <= 32