Apple II User Manual

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Dr. Dobb's Journal, November/December 1976, page 57.

ERRATA FOR RANKIN'S 6502

FLOATING POINT ROUTINES

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