Retro1.org codex

*DECK     SSBFPB
          IDENT  SSBFPB 
          ENTRY  SSBFPB 
          TITLE  SSBFPB - FIND PRIORITY BIT.
*COMMENT  FIND PRIORITY BIT.
 SSBFPB   SPACE  4,10 
***       SSBFPB- FIND PRIORITY BIT.
* 
*         S. H. FISCHER.     81/07/16.
          SPACE  4,10 
***       SSBFPB IS A ROUTINE TO EFFICIENTLY FIND THE FIRST BIT SET 
*         IN A WORD TO THE RIGHT OF BIT 48. THE VALUE RETURNED IS 1 
*         FOR BIT 47, 2 FOR BIT 46 ETC. 49 IS RETURNED FOR ALL BITS 
*         CLEAR.
          SPACE  4,10 
***       SYMPL  CALLING SEQUENCE.
* 
*         SSBFPB( WORD, BITN).
* 
*                WORD = WORD TO FIND BIT IN.
* 
*                BITN = BIT NUMBER RETURNED.
 FPB      SPACE  4,10 
 SSBFPB   EQ     *+1S17D
 FPBX     EQU    *
          SA2    X1          WORD 
          SA1    A1+1        ADDRESS TO RETURN BIT
          PX2    B0          GENERATE LEGAL EXPONENT
          NX2,B7 X2          FIND BIT 
          SX6    B7+1 
          SA6    X1          STORE BIT NUMBER 
          EQ     FPBX        RETURN 
          END