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996
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1
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2 lib2.i contains general-purpose library routines that are not included
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3 in the standard library.
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4
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5 The first section, with entry at lines (2000), (2010) and (2020),
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6 was written for the Life program. Line (2000) is the entry point
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7 for a decrement routine setting .1 <- .1 minus #1. This is very
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8 similar to the increment routine (1020) in the system library,
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9 which I also use. Line (2010) is the decrement and branch on zero
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10 operation. It decrements .1, then if .1 is not zero returns to the
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11 calling point, but if .1 is zero pops an additional entry off the
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12 RESUME stack and returns to that point instead. Line (2020) is an
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13 alternative entry point to the (1020) routine which performs an add
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14 bit operation. It sets .1 <- .1 plus .2, where .2 is already known
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15 to be either #0 or #1.
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16
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17 For the pi and primes programs I added the (2030) routine, which
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18 performs a 16-bit division with remainder. It is faster than the
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19 (1040) routine for two reasons: First, it is a true 16-bit version,
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20 whereas the (1040) routine just shifts over its operands and then
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21 calls the 32-bit division routine (1550). Second, the (1550) routine
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22 generates a remainder as part of the computation, but then simply
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23 throws it away. I needed the remainder, so I have my (2030) routine
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24 return it in .4 and the quotient in .3. In other respects this is
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25 just a 16-bit translation of the (1550) routine.
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26
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27 (2040) and (2049) are entry points to an exponentiation routine that
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28 raises .1 to the .2 power and returns the answer in :1. If entered
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29 through (2040) the routine dies with an error on overflow. If entered
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30 through (2049) then .4 is set to #2 if there is an overflow, otherwise
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31 .4 is set to #1. There is a more detailed description of how this
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32 routine works on the web page.
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33
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34 Louis Howell
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35 May 27, 1996
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