*****    ***         *     *   ****   *****  *****   ***
         *       *   *        **    *  *    *    *    *      *   *
         *          *         * *   *  *    *    *    *      *
         ****      *    ****  *  *  *  *    *    *    ***     ***
             *    *           *   * *  *    *    *    *          *
             *   *            *    **  *    *    *    *      *   *
         ****    *****        *     *   ****     *    ******  ***

         Volume 3 Number 11      48/39/38            November 1978

                     Newsletter of the SR-52 Users Club
                                published at
                           9459 Taylorsville Road
                              Dayton, OH 45424
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

More on the Revealed Firmware (V3N10p4)
     Dix Fulton (83) and Gordon Wilk (1089) have been delving into
Steffen's discovery, producing several new findings.
     Gordon has narrowed a valid calling sequence to:  Pgm 12 SBR 333
R/S D.MS, explaining that "... The SBR address may be any address out-
side of the current user partition and beyond the end of the called
program.  Other (non-Op) functions may be substituted for D.MS if their
address in firmware is greater than the last step in the current par-
tition."  Pgm 12 is only 155 steps, and D.MS starts at step 303 in
firmware (ROM), so a partition of 239 or less will work for this call-
ing sequence.  A list or LRN SST ... begins at the ROM step correspon-
ding to the current user memory (RAM) step prevailing at the call.  For
example, at 59 turn-on key 9 Op 17 GTO 111 PGM 12 SBR 155 R/S P/R LRN
and find ROM step 111 displayed.  Gordon goes on to explain that fol-
lowing the R/S in the calling sequence "... the calculator seems to
execute something in the program as well as Stflg 9 EE SBR* since when
it stops it is expecting a register address where it will find the pro-
gram address or label to search.  If the key at this point in one of
the programs in (revealed) ROM it will set the IAR to this step - in
RAM, if the current partition goes that far, or in ROM if the current
partition is too short.  If any other (non-numeral) key is pressed
there is a label search ending at the end of the partition."  I tend
to agree with Gordon's explanation, except for the last statement.  It
appears that several seconds of some processing (which may or may not
be label searching) goes on following the keying of a non-revealed ROM
function, followed by execution of RAM beginning at the step current at
the call.  Gordon continues with:  "Since user RAM, firmware ROM and
library programs all seem to begin at step 000, the IAR must actually
be wider than the 3 digits of the displayed program counter.  Pgm nn
and the keys accessing firmware must set a value in a base register
which is added to the displayed program counter to arrive at the real
machine address for the IAR.  Further, there must be some way of trans-
lating the keycode or program number into, respectively, starting
address and base.  Perhaps this is by searching registers to find an
indirect address.  Since steps 384-487 in firmware are 13 registers and
there are 13 programs in this firmware, these are addresses and labels -
the code is certainly not obvious."  The code is, indeed, not obvious.
Anyone care to attempt a translation?
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  The SR-52 Users Club is a non-profit loosely organised group of TI PPC owners/users
  who wish to get more out of their machines by exchanging ideas.  Activity centers
  on a monthly newsletter, 52-NOTES edited and published by Richard C Vanderburgh
  in Dayton, Ohio.  The SR-52 Users Club is neither sponsored nor officially sanctioned
  by Texas Instruments, Inc.  Membership is open to any interested person:  $6.00
  includes six future issues of 52-NOTES; back issues start June 1976 @ $1.00 each.
     Dix notes that nothing in either the D.MS or INV D.MS code explains
the rounding which occurs on a fix n display.  Indeed, if the revealed
D.MS or INV D.MS code is keyed into RAM and executed, there is no
rounding.  Upon inspection of the code containing the 2 HIR 20 instruc-
tions, Dix found that as executed in ROM, HIR 20 appears to behave in
3 ways:  rtn, Nop, and GTO*.  He arrived at this conclusion by suggest-
ing "... that Op 12, Op 14, and Op 15 all cause execution to begin at
location 000, with a HIR 20 jump from location 045/046 to location 058
for Op 14, and HIR 20 behaving as a Nop for Op 15.  Similar behavior
must occur for the HIR 20 at 082/083, enabling Op 11 and x to share
the same code."  However, it would seem that for HIR 20 to function
only as a GTO* instruction would be consistent with all the observed
behavior.  Assuming that each of the 3 Op functions initializes the
HIR 20 GTO* pointer before execution, Op 12 would specify 57, causing
a transfer at step 045/046 to the rtn at step 57, Op 14 would specify
58, and Op 15 47.  Similarly, x could specify 57 (or any other step
containing a rtn instruction), and Op 11 84.
     I find that at least one of the revealed-ROM functions: INV D.MS
sometimes performs arithmetic at a higher precision when executed in
RAM.  For example, ROM D.MS INV D.MS on 2.5614 produces 2.561399999920
while when executed in RAM produces 2.561399999999.  The intermediate
2.937222222222 following D.MS on 2.5614 is the same either way.  This
difference in precision suggests either that the arithmetic unit inter-
prets ROM code differently than the same RAM code, or that ROM arith-
metic is performed in a separate arithmetic unit.  The same HIR stack
is used either way, but the residuals in HIRs 1, 2, and 8 differ when
ROM and RAM INV D.MS results differ.
     The D.MS code does confirm the algorithm suggested in V3N7p5 to
determine the H8 residual, and the INV D.MS code can be used to answer
the question of the H2 and H8 residuals.

Fast Number Base Conversion Routines (V3N9p5)
     Bill Skillman (710) has addressed the base ten to base 8 problem
for integers, and devised one approach for the 59/PC using prestored
values for base 8 characters to speed up processing.  Although such
table-lookup schemes can be helpful in speeding execution in some
applications (see some of the faster calendar printers in recent 52-
NOTES), they may not be very effective for fast number base conversions.
It turns out that the straight forward iterative reduction by division
with repeated separation of quotient and remainder, of a base ten num-
ber (integer) by base b is considerably shorter and faster than Bill's
method, especially if        the          output base b number is
processed one numeral at a time.
     In this discussion I use the word numeral to designate a "place"
in the positional representation of numbers, avoiding the use of "digit"
which implies limitation to one of the 0-9 symbols.  For example, the
largest base sixteen numeral is usually denoted by F, but would appear
as 15 in a base ten display.  MSN means most significant numeral; LSN
least significant numeral.
     Here is a short fast (but slower than base b to base ten (V3N9p5)
base ten to base 8 integer converter written for the 58/59, but easily
modified for the 56 or 57:  LA S0 CP CLR R0 L1' ÷ 8 - Int S0 = X 8 =
Pause R0 INV x=t 1' R/S.  Key the base ten integer, press A and see the

                              52-NOTES V3N11p2
corresponding base 8 numerals pause-displayed from LSN to MSN.  Con-
version of positive reals is just as straight forward, provided the
integer and fractional parts are input separately.  For example:
LB X = - Int Pause = GTO B may be added to routine a, and run with
an R/S or B after the base ten fraction has been keyed.  The corres-
ponding base 8 fraction is paus-displayed, one numeral at a time,
starting with the MSN, and continuing indefinitely to the right of
the radix point until stopped with R/S.  For example, to convert the
base ten real:  123456789.123456789 to base 8, key the integer part,
press A, and see pause-displayed:  5,2,4,6,4,7,6,2,7 representing the
base 8 integer:  726746425.  Then key the fractional part, press R/S,
and see:  0,7,7,1,5,3,3,5,1,5,6,3,4,5,4,3,2, ... representing the
base 8 fraction:  .07715335356345432 ... .
     Generalizing these routines to handle other number bases in
addition to octal is easy enough, and does not slow execution speed
perceptibly.  For example:  LE S1 R/S LD CP S0 L1' R0 ÷ R1 - Int S0
= X R1 = Pause R0 INV x=t 1' R/S L2' X R1 - Int Pause = GTO 2' LB 1
S0 CLR R/S L3' X R0 ÷ R1 Prd00 0 R/S GTO 3' LB' R1 S0 CLR R/S L4' ÷
R0 + R1 Prd00 0 R/S GTO 4' handles conversions both ways, and is run
by first keying the base (positive integer), and pressing E.  (Do this
once per base specification).  For base ten to base b, key the integer
part, press D, and see the base b integer pause-displayed numeral by
numeral, beginning with the LSN.  Key the fractional part, press R/S,
and see the base b fraction pause-displayed numeral by numeral begin-
ning with the MSN; stop with R/S.  For base b to base ten, initialize
by pressing B, then input each numeral of the integer part (2 or more
digits for b greater than ten), followed by R/S, starting with the
LSN; end with =, and see the entire (up to ten-place) base ten equi-
valent integer displayed.  Key each numeral of the fractional part,
followed by R/S, starting with the MSN; end with =, and see the entire
base ten equivalent fraction.
     When designing such routines for printer connection, the user
needs to trade the relative advantages of speed versus paper economy:
The fastest will use the most paper (and not be so easy to read) as
slower routines which pack the input or output base b numerals before
printing them.  58/59/PC routines designed for base ten to base six-
teen conversion could output 4 groups of 4-numeral hex characters,
closely resembling the memory dump format of many computers.  Expedi-
ting input for the inverse operation:  Hex to ten poses somewhat of a
problem, although use could be made of the A-E and A' keys for the
A-F numerals.
     Members are invited to share their best number base conversion
programs, especially much-used special-purpose ones which work well
in real-world applications, and demonstrate useful programming

Friendly Competition
     In June 1977 when the new 58/59 machines had been announced, I
stated that HP would have to catch up before the 58/59 could fairly
enter the Friendly Competition arena (V2N6p4).  Now I find an area:
execution speed, where the 58/59 may be hard put to match the HP-67,
since some arithmetic is faster on the HP-67.  This came to my atten-
tion when I translated an optimized Factor Finder program written for
the 67 (PPC Journal V5N2p22) into 59ese, and found that it took about
twice al long to run on a 59!

                              52-NOTES V3N11p3
     It turns out that for large numbers, finding the prime factors
of one integer is harder and more time consuming than finding the
greatest common divisor of 2 integers, or testing an integer for
primality.  Quite a few shortcuts have been devised, with perhaps
the most comprehensive analysis of factoring techniques under one
cover written by Donald Knuth in Vol II of his "The Art of Computer
Programming".  But most methods in the literature work best on large
fast machines, processing very large numbers.  A method which lends
itself well to PPC mechanization first tests an input integer for
division by 2, 3, and 5, dividing out by these factors and their
multiplicities if/when there is no remainder.  Successive divisions
are performed using increasingly larger divisors, skipping those
which are multiples of those already tried, until the divisor exceeds
the square root of the remaining integer.  For HP-67 implementation,
the code exercised the most often takes the form:  R2 R3 ÷ Frac x=0
GSB 0 RC S+3, which takes about .38 seconds to execute.  Corresponding
59 code looks like:  R2 ÷ R3 = INV Int x=t 1' 4 SUM 3, which takes
about .53 seconds to execute.
     So the challenge is to beat J L Horn's HP-67 program, which he
claims proves 9999999967 prime in 2 hours 55 minutes (worst case for
a maximum of ten digits).  A smaller test case supplied by Lynn
Yarbrough (1081) with a 58 Factor Finder "assembled" by a program he
wrote in SNOBOL, is to factor 987654321 into 3,3,17,17,379721.  Lynn's
program takes about 5 minutes, Horn's about 1 minute, and the follow-
ing 58/59/PC program adapted from one Mike Louder (53) wrote for the
52 (65-Notes V3N4p9) takes about 2 minutes.  This turned out to be
slightly faster than my 59 version of Horn's 67 program.

TI-58/59/PC Program:  Speedy Factor Finder          Mike Louder(53)/Ed

User Instructions:  Key  a positive integer, press E.  See printed
input confirmation, and the prime factors.

Program Listing:

000:  R/S LC SUM2 R1 ÷ R2 = INV Int x=t 2' rtn L3' CP 6 C 4 C 2 C 4 C
027:  2 C 4 C 6 C 2 C R2 x:t R3 x≥t 3' R1 Prt Adv Adv Adv CLR RST
051:  L2' R1 ÷ R2 Prt = S1 √x S03 0 GTO C LE CP S1 Prt Adv √x S03 1
079:  S02 1 C 1 C 2 C 1 S02 GTO 3'
                          - - - - - - - - -

Repeating Decimals (V3N10p5)
     George Hartwig (638) and Samuel Allen (1032) note that a repeating
decimal:  .a1 a2 ... an a1 a2 ... may be written in rational fraction
form as:  (a1 a2 ... an)/(99 ... 9), where the denominator is composed
of n 9s.  Samuel notes further that "If a decimal fraction repeats only
after a certain number of places, it may be broken up into the repeat-
ing part plus the non-repeating part, the two expressed as rational
fractions and added; this .abcdefgefg... could be expressed as the sum
of abcd/10000 and efg/9990000" which generalizes to:
.a1 a2 ...an b1 b2..bm b1..=((a1 a2 ...an)/10n) + ((b1 b2 ...bm)/
(99...900...0), where the denominator of the second term is composed of
m nines and n zeros.  These 2 terms combine to:  ((99...9)(a1 a2 ...an)
+ (b1 b2 ...bm))/ (99...90...0).

                              52-NOTES V3N11p4
     When both the numerator and denominator are short enough to fit
in a PPC register, reduction of the rational fraction to lowest terms
is quick and easy via Euclid's Algorithm (which finds the greatest
common divisor (GCD) of 2 integers).  For example, .865259740259740...
may be expressed as 865258875/999999000, which reduces via the GCD of
1623375 to 533/616:  Key the denominator, press A; key the numerator,
press R/S, and see the GCD in about 8 seconds, using the following
58/59 mechanization of Euclid's Algorithm:  LA CP S1 ÷ R/S S2 L1' =
INV Int x=2 2' X R2 S1 = EE INV EE S2 R1 ÷ R2 GTO 1' L2' R2 R/S.
     But if a numerator or denominator is too big to fit in a PPC reg-
ister, reduction to lowest terms would require extended precision
arithmetic, which in a 59 might be made to handle up to 500-digit
numbers, but would be slow.  So for long-cycle cases, other methods
might be more attractive.  One way is to take a quasi-brute-force
approach:  Start with the minimum which the denominator can be (one
larger than the number of digits in the repetition cycle), and a
numerator the nearest integer to half the denominator.  Divide, and
compare with a full-register representation (truncated 13 MSDs for the
58/59) of the repeating decimal.  If the result is too large, cut the
numerator in half, if too small, increase it by half.  Compare, and
repeat the process, taking the mean of bracketing numerators until
either a perfect comparison occurs (stop), or the brackets meet, in
which case add one to the denominator and start again with a new half-
denominator numerator.  If (as is likely) the input repeating decimal
cycle is longer than a full-register length, test the results with an
infinite-division routine (V3N10p5).  If the results are incorrect,
add one to the last denominator and start again.  An upper limit for
this approach using a 52/56/58/59 would appear to be a repeating deci-
mal whose cycle length is around 1012 digits, and whose rational
fraction lowest-term denominator is the smallest it can be.
     This method is quick when the denominator of the rational fraction
is at or close to the minimum, but very slow for cases like 533/616,
where the minimum denominator appears to be 7, although the 3-digit
preface to the first repetition cycle argues somewhat intuitively for
a larger minimum denominator.  But how much larger?
     On the other hand, this method is very quick to determine that
a 1570-digit repeating decimal cycle which begins with 8650541056651...
and ends with ...9847231063017 is equivalent to the rational fraction
1359/1572:  Prestore the 13 MSDs in Reg 1, key the minimum denominator
(1571), press A, and get the printed (numerator in T, denominator dis-
played if no printer) rational fraction in 17 seconds with the follow-
ing routine:

000:  LA S2 L5' S04 0 S3 L1' R1 x:t R3 ÷ R4 = ÷ 2 = Int S5 ÷ R2 = x≥t
033:  2' R5 - Exc3 = CP x=t 3' GTO 1' L2' x=t 4' R3 x:t R5 x=t 3' S4
058:  GTO 1' L3' Op22 R2 GTO 5' L4' R5 Prt x:t R2 Prt Adv Adv Adv R/S

This contrasts with more than 17 minutes required to find that a 78-
digit cycle beginning with 8662420382165... and ending with ...
2611464968152 is equivalent to 136/157.  But my guess is that using the
Euclid Algorithm approach with extended precision arithmetic wouldn't
be any faster, especially considering the time required to input 156
digits (correctly!).  Members are invited to explore repeating decimals
further, and to share their discoveries, insights, etc.

                              52-NOTES V3N11p5
Tips and Miscellany
     Calculator RF Interference:  Brian Agron (954) notes that Federal
Aviation Regulation 91.19 prohibits the use of any electronic device
on most flights unless the device does not interfere with navigation
or communications.  This would appear to put the burden of proof on
the user.  Brian also passes along a clip from FLYING (Sept 1978)
which indicates that the Canadian government has determined that 5
different calculators, each operated within 3 feet of an ADF loop
antenna, seriously interfered with reception in the 200-450 KHz band.
PPC operation in the cabin of an airliner is probably too far from
sensitive flight equipment to do any harm, but operation in the cock-
pit of any aircraft might cause trouble.  So when in doubt, check out
an intended configuration of calculator and avionics before flying.
     Used SR-52s and SR-56s:  S G Allen (1032) would like to buy
"... used SR-51s and SR-56s for resale to my students at Manhattan
Community College at cost."
     Oil and Gas Well Accounting and Taxes:  L H Southmayd (1097)
would like to make contact with other members interested in programming
in these applications areas.
     PC Battery Charging:  Several members have noted that the PC-100A
can easily overcharge an installed battery pack, since charging occurs
even with the power switch off.  This problem was covered in V2N5p3,
along with the suggestion that members wishing to try hardware mods
to provide more charging control contact Bob Edelen (100).
     Games Buffs:  Walter Fair (1056) enjoys programming games, and
invites other interested members to contact him.  Incidently, members
with specific applications interests/problems may find it worth looking
through back issues of 52-NOTES to identify likely correspondents from
their contributed material.  Be sure you are up to date with membership
address changes before writing.
     PC Roller Cleaning:  The question came up recently, but TI has no
specific recommendation for cleaning the rubber roller in the paper
drive mechanism.  A typewriter roller-cleaning solvent should do, but
in any case, don't let the solvent contact the printheads.
     More on Op3mn on 2-Digit Registers (V3N9p5):  Bill Skillman (710)
and Maurice Swinnen (779) note that the reg 40 exception (V2N12p2)
applies.  Maurice further notes that Dsz*mn ab works for all registers,
as expected (V2N7p6).
     CROM Calls to Undefined Labels:  Steve Bepko (45) notes that at
turn-on, a call to ML-09 D puts the pointer "out of bounds", such that
LRN key cycling will not switch to LRN mode.  It appears that the
... Pgm 00 A' ... sequence at steps 062-064 causes the hangup, since
A' is undefined in Pgm 00 (user memory).  But as Steve points out, a
call to a similar sequence in ML-08 (Pgm 8 E) doesn't disable the LRN
function, and neither does a call directly to Pgm 9 SBR 062 or PGM 8
SBR 055.  It seems that the ML-09 call to its own routine E at step
061 before trying to call Pgm 00 A' makes the difference, but why?
(Before trying Pgm 8 E, initialize Reg 2 so its contents is greater
than that of Reg 1, to avoid invoking a confusing overflow signal).
     Membership Address Changes:  544:  863 Post Ave Rochester, NY
14169; 938:  3418 El Potrero Dr Bakersfield CA 93304; 973:  81 Stanton
Rd Brookline, MA 02146.

                              52-NOTES V3N11p6 (end)