Retro1.org codex

*DECK     SSBSBF
PROC SSBSBF (TABLE, ORD, BIT, LEN, SOURCE); 
# TITLE SSBSBF - STORE BITFIELD IN A TABLE.                        #
 
      BEGIN  # SSBSBF # 
# 
**    SSBSBF - STORE BITFIELD IN A TABLE. 
* 
*     D. G. DEPEW.           81/10/26.
* 
*     PROC SSBSBF (TABLE, ORD, BIT, LEN, SOURCE)
* 
*     ENTRY    TABLE = ARRAY INTO WHICH DATA IS TO BE STORED. 
*                ORD = WORD ORDINAL WITHIN TABLE WHERE BITFIELD STARTS. 
*                BIT = STARTING BIT POSITION WITHIN THE WORD (SYMPLESE).
*                LEN = NUMBER OF BITS TO STORE (RANGE:  1 TO 60). 
*             SOURCE = DATA TO BE STORED, RIGHT JUSTIFIED IN A CM WORD. 
* 
*     EXIT     TABLE = THE SPECIFIED BITFIELD CONTAINS THE RIGHTMOST
*                      *LEN* BITS OF *SOURCE*.  THE RIGHTMOST BIT OF
*                      *SOURCE* ALIGNS WITH THE RIGHTMOST BIT OF THE
*                      BITFIELD, EVEN IF A WORD BOUNDARY IS SPANNED.
*                ORD = INCREMENTED BY 1 IF THE BITFIELD SPANS A WORD
*                      BOUNDARY.
*                BIT = FIRST BIT POSITION AFTER THE STORED BITFIELD.
*                LEN = UNCHANGED. 
*             SOURCE = UNCHANGED. 
* 
*     NOTES   RESULT IS UNPREDICTABLE IF LEN IS OUT OF RANGE. 
*             IF THE SPECIFIED BITFIELD SPANS A WORD BOUNDARY, THE
*               OVERFLOW BITS ARE STORED INTO THE NEXT CONSECUTIVE CM 
*               WORD.  THAT IS, NO CONSIDERATION IS MADE FOR SYMPL
*               PARALLEL ARRAYS OR FOR ARRAYS WITH AN ENTRY SIZE
*               GREATER THAN ONE. 
# 
 
      ARRAY TABLE [00:00] S(1);  #TABLE CONTAINING BITFIELD            #
        ITEM T$WD       U(00,00,60);
 
      ITEM ORD;              #WORD WITHIN TABLE                        #
      ITEM BIT;              #STARTING BIT WITHIN WORD                 #
      ITEM LEN;              #LENGTH OF BITFIELD                       #
      ITEM SOURCE  U;        #WORD THAT CONTAINS DATA                  #
 
      ITEM THIS;             #NUM OF BITS TO STORE IN SPECIFIED WORD   #
      ITEM NEXT;             #NUM OF BITS TO STORE IN FOLLOWING WORD   #
 
 
 
 
 
      IF (BIT + LEN) GR 60
      THEN                   # WORD BOUNDARY IS SPANNED                #
        BEGIN 
        THIS = 60 - BIT;
        NEXT = BIT + LEN - 60;
        B<BIT,THIS> T$WD[ORD] = SOURCE  / 2 ** NEXT;
        B<0,NEXT> T$WD[ORD + 1] = SOURCE; 
        ORD = ORD + 1;
        BIT = NEXT; 
        END 
      ELSE                   # WORD BOUNDARY NOT SPANNED               #
        BEGIN 
        B<BIT,LEN> T$WD[ORD] = SOURCE;
        IF (BIT + LEN) EQ 60
        THEN                 # BITFIELD ENDS ON WORD BOUNDARY          #
          BEGIN 
          ORD = ORD + 1;
          BIT = 0;
          END 
        ELSE                 # SIMPLEST CASE                           #
          BIT = BIT + LEN;
        END 
 
      END  # SSBSBF # 
 
      TERM