Altair BASIC 3.2 (4K)

2.12 RND - Optional Function #2

Rnd

Generates a random number. This is a bit odd... like all inline functions it takes a numeric argument, but in RNDs case this argument is mostly ignored. If it's a negative number it skips a couple of stages of reseeding RND_SEED.

If tghe argument in FACCUM is negative, then skip over the

0C5F EF Rnd RST FTestSign

0C60 FA7C0C JM 0C7C

Load the seed into FACCUM.

0C63 21910C LXI H,RND_SEED

0C66 CD0F0A CALL FLoadFromMem

0C69 C8 RZ

Multiply seed by 11,879,546.

0C6A 013598 LXI B,9835

0C6D 117A44 LXI D,447A

0C70 CDE508 CALL FMul+2

Add 0.00000003927678

0C73 012868 LXI B,6828

0C76 1146B1 LXI D,B146

0C79 CD1208 CALL FAdd+2

Swap first and third mantissa bytes.

0C7C CD1D0A CALL FCopyToBCDE

0C7F 7B MOV A,E

0C80 59 MOV E,C

0C81 4F MOV C,A

Set FTEMP_SIGN to 0x80 to indicate to FNormalise that it doesn't need to change the sign. Also set FACCUM's exponent to 0 so the result, when normalised, will be less than 1.

0C82 3680 MVI M,80

0C84 2B DCX H

0C85 46 MOV B,M

0C86 3680 MVI M,80

0C88 CD5E08 CALL FNormalise+3

Exit via a copy of the result to RND_SEED so it can be used for the next time RND is called.

0C8B 21910C LXI H,RND_SEED

0C8E C3290A JMP FCopyToMem

Seed for random number generation.

0C91 52C74F80 RND_SEED 0.811635

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