Version analysis of log - Elite on the BBC Micro and NES

This code appears in the following versions (click to see it in the source code):

6502 Second Processor and Master

Code variations between these versions are shown below.

       Name: log
       Type: Variable
   Category: Maths (Arithmetic)
    Summary: Binary logarithm table (high byte)


 At byte n, the table contains the high byte of:

   &2000 * log10(n) / log10(2) = 32 * 256 * log10(n) / log10(2)

 where log10 is the logarithm to base 10. The change-of-base formula says that:

   log2(n) = log10(n) / log10(2)

 so byte n contains the high byte of:

   32 * log2(n) * 256


.log

 SKIP 1

 FOR I%, 1, 255

  B% = INT(&2000 * LOG(I%) / LOG(2) + 0.5)

  EQUB B% DIV 256

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