www.delorie.com/gnu/docs/binutils/as_288.html   search  
Buy GNU books!

Using as

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ] Compare-and-Branch

The 960 architectures provide combined Compare-and-Branch instructions that permit you to store the branch target in the lower 13 bits of the instruction word itself. However, if you specify a branch target far enough away that its address won't fit in 13 bits, the assembler can either issue an error, or convert your Compare-and-Branch instruction into separate instructions to do the compare and the branch.

Whether as gives an error or expands the instruction depends on two choices you can make: whether you use the `-no-relax' option, and whether you use a "Compare and Branch" instruction or a "Compare and Jump" instruction. The "Jump" instructions are always expanded if necessary; the "Branch" instructions are expanded when necessary unless you specify -no-relax---in which case as gives an error instead.

These are the Compare-and-Branch instructions, their "Jump" variants, and the instruction pairs they may expand into:

        Compare and
     Branch      Jump       Expanded to
     ------    ------       ------------
        bbc                 chkbit; bno
        bbs                 chkbit; bo
     cmpibe    cmpije       cmpi; be
     cmpibg    cmpijg       cmpi; bg
    cmpibge   cmpijge       cmpi; bge
     cmpibl    cmpijl       cmpi; bl
    cmpible   cmpijle       cmpi; ble
    cmpibno   cmpijno       cmpi; bno
    cmpibne   cmpijne       cmpi; bne
     cmpibo    cmpijo       cmpi; bo
     cmpobe    cmpoje       cmpo; be
     cmpobg    cmpojg       cmpo; bg
    cmpobge   cmpojge       cmpo; bge
     cmpobl    cmpojl       cmpo; bl
    cmpoble   cmpojle       cmpo; ble
    cmpobne   cmpojne       cmpo; bne

  webmaster     delorie software   privacy  
  Copyright 2003   by The Free Software Foundation     Updated Jun 2003