source: trunk/minix/lib/i386/em/em_fef4.s@ 20

.sect .text; .sect .rom; .sect .data; .sect .bss
.define .fef4

        .sect .text
.fef4:
                                ! this could be simpler, if only the
                                ! fxtract instruction was emulated properly
        mov     bx,sp
        mov     ax,8(bx)
        and     ax,0x7f800000
        je      1f              ! zero exponent
        shr     ax,23
        sub     ax,126
        mov     cx,ax           ! exponent in cx
        mov     ax,8(bx)
        and     ax,0x807fffff
        or      ax,0x3f000000   ! load -1 exponent
        mov     bx,4(bx)
        mov     4(bx),ax
        mov     (bx),cx
        ret
1:                              ! we get here on zero exp
        mov     ax,8(bx)
        and     ax,0x007fffff
        jne     1f              ! zero result
        mov     bx,4(bx)
        mov     (bx),ax
        mov     4(bx),ax
        ret
1:                              ! otherwise unnormalized number
        mov     cx,8(bx)
        and     cx,0x807fffff
        mov     dx,cx
        and     cx,0x80000000
        mov     ax,-125
2:
        test    dx,0x800000
        jne     1f
        dec     ax
        shl     dx,1
        or      dx,cx
        jmp     2b
1:
        mov     bx,4(bx)
        mov     (bx),ax
        and     dx,0x807fffff
        or      dx,0x3f000000   ! load -1 exponent
        mov     4(bx),dx
        ret