usr/src/cmd/lisp/dsneg.s

        .globl  _dsneg
#
#       dsneg(top, bot);
#       int *top, *bot;
#
#       routine to destructively negate a bignum stored in array format
#       lower order stuff at higher addresses. It is assume that the
#       result will be positive.
#
_dsneg: .word   0
        movl    4(ap),r1        #load up address.
        clrl    r2              #set carry
loop:   mnegl   (r1),r0         #negate and take carry into account.
        addl2   r2,r0
        extzv   $0,$30,r0,(r1)
        extv    $30,$2,r0,r2
        acbl    8(ap),$-4,r1,loop
                                #decrease r1, and branch back if appropriate.
        ret