base:errata_for_rankin_s_6502_floating_point_routines

# ERRATA FOR RANKIN'S 6502 FLOATING POINT ROUTINES

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

base/errata_for_rankin_s_6502_floating_point_routines.txt · Last modified: 2015-04-17 04:31 by 127.0.0.1