You are correct. the conversion to Celsius * 10 is done earlier on, because it is easy to optionally perform this conversion, and it's easy to render the various formats (positive/negative/DP,no DP) of it to the 7-segment display banks.
Also worth considering that I originally had no interest in fahrenheit (I live in the UK). This was done as an extra later on. Didn't want to poo the original implementation taking fahrenheit straight off the sensors.
OK, I understand. The approach works even better if you multiply by 10:
int16_t celsius2fahrenheit10(int16_t c)
{
int16_t f = 0;
f += c << 4;
f -= c;
f -= c >> 1;
f -= c >> 3;
f += c >> 5;
f += 320 * 8;
f >>= 3;
return f;
}
It's really interesting to see that it could be done like that, but, that pseudo code you've given me would translate to a heck of a lot of MCS-48 instructions! 16-bit subtraction in particular is really expensive. Potentially not much gain there?
This is the same code in MCS48 assembly. Or so I hope.
; INPUT: r1:r0 celsius * 10
; OUTPUT: r3:r2 fahrenheit * 10
MOV A, r0
ADD A, r0
MOV r2, A
MOV r4, A
MOV A, r1
RLC A
MOV r3, A
MOV r5, A
MOV A, r4
ADD A, r4
XCH A, r5
RLC A
MOV r4, A
MOV A, r2
ADD A, r5
XCH A, r3
ADDC A, r4
MOV r2, A
MOV A, r5
ADD A, r5
XCH A, r4
RLC A
MOV r5, A
MOV A, r3
ADD A, r4
XCH A, r2
ADDC A, r5
MOV r3, A
MOV A, r1
ADD A, r1
MOV A, r1
RRC A
MOV r5, A
MOV A, r0
RRC A
MOV r4, A
MOV A, r5
ADD A, r5
MOV A, r5
RRC A
XCH A, r4
RRC A
MOV r5, A
MOV A, r2
ADD A, r5
XCH A, r3
ADDC A, r4
MOV r2, A
MOV A, r4
ADD A, r4
MOV A, r4
RRC A
XCH A, r5
RRC A
MOV r4, A
MOV A, r3
ADD A, r4
XCH A, r2
ADDC A, r5
MOV r3, A
MOV A, r5
ADD A, r5
MOV A, r5
RRC A
XCH A, r4
RRC A
MOV r5, A
MOV A, r4
ADD A, r4
MOV A, r4
RRC A
XCH A, r5
RRC A
MOV r4, A
MOV A, r2
ADD A, r4
XCH A, r3
ADDC A, r5
ADD A, 10
MOV r2, A
ADD A, r2
MOV A, r2
RRC A
XCH A, r3
RRC A
MOV r2, A
MOV A, r3
ADD A, r3
MOV A, r3
RRC A
XCH A, r2
RRC A
MOV r3, A
MOV A, r2
ADD A, r2
MOV A, r2
RRC A
XCH A, r3
RRC A
MOV r2, A
But you do have CPL -- that does not help? Anyway, without subtraction, you could do the very same with one additional add:
int16_t celsius2fahrenheit(int16_t c)
{
int16_t f = 0;
f += c << 1;
f += c << 2;
f += c << 3;
f += c >> 2;
f += c >> 3;
f += c >> 5;
f += 320 * 8;
f >>= 3;
return f;
}
Also worth considering that I originally had no interest in fahrenheit (I live in the UK). This was done as an extra later on. Didn't want to poo the original implementation taking fahrenheit straight off the sensors.