AA START
 ;; GR1 * 2^GR2 + GR3 * 2^GR4 --> GR5 * 2^GR6
 ;; GR1*2^(GR2-15)  ( 0x7000*2^(3-15); by asir )
 ;; GR5=5400, GR6=0005
  LAD GR1,#7001
  LAD GR2,4
  LAD GR3,#7000
  LAD GR4,3
  CALL FADD
  LD GR1,GR5
  LD GR2,GR6
  CALL FNORM
  RET
FADD LD GR6,GR2
  CPA GR2,GR4
  JMI AAA
  LD GR6,GR2    ;; GR2 >= GR4桁そろえ
  LD GR7,GR2
  SUBA GR7,GR4
  SRL GR3,0,GR7
  JUMP BBB
AAA LD GR6,GR4   ;; GR2 < GR4桁そろえ
  LD GR7,GR4
  SUBA GR7,GR2
  SRL GR1,0,GR7
BBB LD GR5,GR1
  ADDL GR5,GR3
  PUSH 0,GR5
  AND GR5,=#8000  ;;一番上の桁が 1 なら 0 に.
  JZE DDD
  POP GR5
  SRL GR5,1
  ADDA GR6,=1
  RET
DDD POP GR5
  RET
 ;; normailze  GR1=0.1xxxx, GR2 : exponent
FNORM CPA GR1,=0
  JNZ FNORM0
  RET 
FNORM0 LD GR3,GR1
  AND GR3,=#8000
  JZE PPP1
  SRL GR1,1  
  ADDA GR2,=1
  RET   ;; 1xxxx
PPP1 LD GR3,GR1
  AND GR3,=#4000
  JZE PPP2
  RET           ;; 01xxx 
PPP2  SLL GR1,1   ;; 00xxx
      SUBA GR2,=1
      JUMP FNORM0
 END