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3297: THE 'RE-STACK' SUBROUTINE (offset +3D)
Used by the routine at atn.
The routine at RE_ST_TWO continues here.
The address of this routine is found in the table of addresses. It is called via the calculator literal +3D by the routines at CIRCLE, DRAW, exp, ln and get_argt. The routine at RE_ST_TWO also continues here.
This subroutine is called to re-stack one number (which could be a 'small integer') in full five-byte floating-point form.
Input
HL Address of the first byte of the number
Output
re_stack 3297 LD A,(HL) If the first byte is not zero, return - the number cannot be a 'small integer'.
3298 AND A
3299 RET NZ
329A PUSH DE Save the 'other' pointer in DE.
329B CALL INT_FETCH Fetch the sign in C and the number in DE.
329E XOR A Clear the A register.
329F INC HL Point to the fifth location.
32A0 LD (HL),A Set the fifth byte to zero.
32A1 DEC HL Point to the fourth location.
32A2 LD (HL),A Set the fourth byte to zero; bytes 2 and 3 will hold the mantissa.
32A3 LD B,$91 Set B to +91 for the exponent, i.e. for up to 16 bits in the integer.
32A5 LD A,D Test whether D is zero so that at most 8 bits would be needed.
32A6 AND A
32A7 JR NZ,RS_NRMLSE Jump if more than 8 bits needed.
32A9 OR E Now test E too.
32AA LD B,D Save the zero in B (it will give zero exponent if E too is zero).
32AB JR Z,RS_STORE Jump if E is indeed zero.
32AD LD D,E Move E to D (D was zero, E not).
32AE LD E,B Set E to zero now.
32AF LD B,$89 Set B to +89 for the exponent - no more than 8 bits now.
RS_NRMLSE 32B1 EX DE,HL Pointer to DE, number to HL.
RSTK_LOOP 32B2 DEC B Decrement the exponent on each shift.
32B3 ADD HL,HL Shift the number right one position.
32B4 JR NC,RSTK_LOOP Until the carry is set.
32B6 RRC C Sign bit to carry flag now.
32B8 RR H Insert it in place as the number is shifted back one place normal now.
32BA RR L
32BC EX DE,HL Pointer to byte 4 back to HL.
RS_STORE 32BD DEC HL Point to the third location.
32BE LD (HL),E Store the third byte.
32BF DEC HL Point to the second location.
32C0 LD (HL),D Store the second byte.
32C1 DEC HL Point to the first location.
32C2 LD (HL),B Store the exponent byte.
32C3 POP DE Restore the 'other' pointer to DE.
32C4 RET Finished.
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