Routines
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12171: THE 'CA=10*A+C' SUBROUTINE
This subroutine is called by PRINT_FP to multiply each byte of D'E'DE by 10 and return the integer part of the result in the C register. On entry, the A register contains the byte to be multiplied by 10 and the C register contains the carry over from the previous byte. On return, the A register contains the resulting byte and the C register the carry forward to the next byte.
Input
A First number (M)
C Second number (N)
Output
A LSB of 10*M+N
C MSB of 10*M+N
CA_10A_C 12171 PUSH DE Save whichever DE pair is in use.
12172 LD L,A Copy the multiplicand from A to HL.
12173 LD H,0
12175 LD E,L Copy it to DE too.
12176 LD D,H
12177 ADD HL,HL Double HL.
12178 ADD HL,HL Double it again.
12179 ADD HL,DE Add in DE to give HL=5*A.
12180 ADD HL,HL Double again: now HL=10*A.
12181 LD E,C Copy C to DE (D is zero) for addition.
12182 ADD HL,DE Now HL=10*A+C.
12183 LD C,H H is copied to C.
12184 LD A,L L is copied to A, completing the task.
12185 POP DE The DE register pair is restored.
12186 RET Finished.
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