   10 REM"„ƒ*  M  A  X  I  N  F  0  *  œ
   20 REM   Information and instructions for "Maxiply" - program for multiplying very large numbers.
   30 MODE7:VDU23,1,0;0;0;0;
   40 PRINTTAB(3)"ƒMAXINFO - 'MAXIPLY' INFORMATION" 
   50 PRINTTAB(3)"ƒMAXINFO - 'MAXIPLY' INFORMATION" 
   60 PRINT"‘";STRING$(39,"s")
   70 PRINT"†  Seeing the references in 8BS issues  †35 and 36 to a routine for multiplying †large numbers together, called Fermat, †prompted me to haul out, dust down, and†polish up a program originally worked  †out on an MSX."
   80 PRINT"†  This program, called Maxiply, will   †multiply two numbers with, in essence, †an infinite number of digits. The only †limitations are the amount of memory   †available, and the length of time you  †want to run your computer."
   90 PRINT"†  With the memory available on the 32K †Beeb, you can multiply any two numbers †which give an answer up to 3000 digits †long, for example two 1500 digit       †numbers, or a 2900 digit number by a   †100 digit number."
  100 PROCpage
  110 PRINTTAB(13)"ƒMAXINFO 2"
  120 PRINT"‘";STRING$(39,"`"):VDU11
  130 PRINT"†  It doesn't matter whether the larger †number is entered first or second - the†only difference is that if it's entered†second there will be more progress and †time checks displayed."
  140 PRINT"†  The program works by multiplying and †adding in groups, which gets a little  †complicated, but speeds things up. On  †average, it runs about twice as fast as†the Fermat routine, which also seems to†have a size limit.";
  150 PRINT" The program works   †its way through the numbers from left  †to right, to simplify the arrays."
  160 PRINT"†  Most of the program length is taken  †up with input and output routines and  †options, and checking procedures.If you†wanted more memory for even larger     †numbers, you could - carefully - remove†some of these, ";
  170 PRINT"and then just increase  †the DIM's and MAX%."
  180 PROCpage
  190 PRINTTAB(3)"ƒMAXINFO 3 -‚INPUT INSTRUCTIONS 1"
  200 PRINT"‘";STRING$(39,"`"):VDU11
  210 PRINT"1)†Numbers can be entered digit by     †digit, in groups of 238, up to 3000    †digits for the first number, and to    †(3000-1st no. digits) for the second.  †A running total and total left ('max') †is given at each stage.";
  220 PRINT" Each time you  †get to another 238 digits (you can't   †enter more at one go), enter these, and†after a short checking pause, you will †be prompted to continue the number. If †you enter less than 238 digits in any  †section, ";
  230 PRINT"the program will then continue†to either the second number or the     †calculations."
  240 PRINT"2)†You can enter a decimal point at any†stage (this was difficult!) in either  †the first or second numbers, or both,  †and carry on with additional groups of †238 digits.The section with the decimal†point will be 237 digits long."
  250 PROCpage
  260 PRINTTAB(3)"ƒMAXINFO 4 -‚INPUT INSTRUCTIONS 2"
  270 PRINT"‘";STRING$(39,"`"):VDU11
  280 PRINT"3)†You can enter just 'R' for either   †number and you will get a random number†of a random length between 1 and 300   †digits."
  290 PRINT"4)†To get a random number of a specific†length, enter 'R' plus the number of   †digits you want. For example, R1275    †will give you a random number 1275     †digits long."
  300 PRINT"5)†Entering 'R0'(zero) will give you a †random number of a random length       †between 1 and 1200 digits."
  310 PRINT"6)†You can square the first number,    †whether entered directly or as a random†number, by just entering 'S' when      †prompted for the second number."
  320 PRINT"7)†Entering 'I' at the First Number    †prompt will return you to these notes."
  330 PRINT"8)†Escape gives you a new run option."
  340 PROCpage
  350 PRINTTAB(9)"ƒMAXINFO 5 -NOTES 1"
  360 PRINT"‘";STRING$(39,"`"):VDU11
  370 PRINT"ƒ1)†Inputs for the first and second     †numbers can be freely mixed. The first †number, for example, can be direct     †input, and the second a random number."
  380 PRINT"ƒ2)†If you try to enter too many digits †at any stage, you will be told about   †it!"
  390 PRINT"ƒ3)†The checking procedure will remove  †anything that isn't useful, such as    †stray letters, symbols, spaces and     †unwanted zeros. To see this, enter a   †mixture of a few digits and a lot of   †gobbledegook (except commas) ";
  400 PRINT"for the   †first number, and then square it."
  410 PRINT"ƒ4)†Don't worry if a large answer zooms †past at the end. The answer, and the   †original numbers, can be recalled and  †displayed at the end, and there are    †also print options."
  420 PROCpage
  430 PRINTTAB(9)"ƒMAXINFO 6 -NOTES 2"
  440 PRINT"‘";STRING$(39,"`"):VDU11
  450 PRINT"ƒ5)†To get a large answer relatively    †quickly, multiply a very large number  †by a smallish one, rather than two     †similar sized numbers."
  460 PRINT"ƒ6)†To aid rapid direct input, function †keys 0 and 1 hold ten digit numbers."
  470 PRINT"ƒ7)†Squaring a lot of 9's produces      †interesting results, as do 3's and 6's,†and multiplying variations on equal    †numbers of 3's, 6's, and 9's. This is  †also a good quick test of whether the  †program is working properly!"
  480 PRINT"ƒ8)†If you did a multiplication on a    †(rather large) piece of paper which    †had an answer 3000 digits long, that   †answer would be over sixty feet long.  †And it would only take about a year..."
  490 PRINT"‘";STRING$(39,"p")
  500 PRINT'"ƒPRESS:‡SPACE†to run Maxiply.                  ‡I†to repeat Information.";
  510 G$=GET$
  520 IF G$="I" RUN ELSE CHAIN"MAXIPLY"
  530 DEFPROCpage
  540 PRINT"‘";STRING$(39,"p")
  550 PRINTTAB(24)"PRESS SPACE";
  560 G=GET:CLS
  570 ENDPROC