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base:errata_for_rankin_s_6502_floating_point_routines [2015-04-17 04:31] (current)
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 +Dr. Dobb's Journal, November/December 1976, page 57.
 +Sept. 22, 1976
 +Dear Jim,
 +Subsequent to the publication of "Floating Point
 +Routines for the 6502" (Vol.1, No.7) an error which I made in
 +the LOG routine came to light which causes improper results
 +if the argument is less than 1.  The following changes will
 +correct the error.
 +1.  After:            CONT JSR SWAP (1D07)
 +    Add:    A2 00          LDX =0    LOAD X FOR HIGH BYTE OF EXPONENT
 +2.  After:                 STA M1+1 (1D12)
 +    Delete:                LDA =0
 +                           STA M1
 +    Add:    10 01          BPL *+3   IS EXPONENT NEGATIVE
 +            CA             DEX       YES, SET X TO $FF
 +            86 09          STX M1    SET UPPER BYTE OF EXPONENT
 +3.  Changes 1 and 2 shift the code by 3 bytes so add 3 to the
 +addresses of the constants LN10 through MHLF whenever
 +they are referenced.  For example the address of LN10 changes
 +from 1DCD to 1DD0.  Note also that the entry point for
 +LOG10 becomes 1DBF.  The routines stays within the page
 +and hence the following routines (EXP etc.) are not affected.
 +Yours truly,
 +Roy Rankin
 +Dep. of Mech. Eng.
 +Stanford University
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