MUMPS - Sample Programs

Sample Programs

The direct execution of source code on historical computing platforms in an era of tiny disks, minuscule RAM and 300 baud serial connections led to a historical coding style that was terse, dense and expert friendly, even as more current MUMPS coding styles produce more readable code.

This is an example of M code from 2010, a solution to a benchmarking exercise based on calculating the longest sequence encountered when calculating the longest sequence of the Collatz conjecture for a range of integers. This example is written in GT.M and exploits and illustrates many features of MUMPS.

threeen1f ; Find the maximum number of steps for the 3n+1 problem for all integers through two input integers. ; See http://docs.google.com/View?id=dd5f3337_24gcvprmcw ; Assumes input format is 3 integers separated by a space with the first integer smaller than the second. ; The third integer is the number of parallel computation streams. If it is less than twice the ; number of CPUs or cores, the parameter is modified to that value. An optional fourth integer is the ; sizes of blocks of integers on which spawned child processes operate. If it is not specified, the ; block size is approximately the range divided by the number of parallel streams. If the block size is ; larger than the range divided by the number of execution streams, it is reduced to that value. ; No input error checking is done. ; Although the problem can be solved by using strictly integer subscripts and values, this program is ; written to show that the GT.M key-value store can use arbitrary strings for both keys and values - ; each subscript and value is spelled out using the strings in the program source line labelled "digits". ; Furthermore, the strings are in a number of international languages when GT.M is run in UTF-8 mode. ; K.S. Bhaskar 2010612 ; No claim of copyright is made with respect to this program. ; Variables do not have to be declared before use, but are New'd in subprograms to ensure that they ; do not conflict with names in the caller. ; The program reads the program source at the label digits to get strings (separated by ;) for each language used. digits ;zero;eins;deux;tres;quattro;пять;ستة;सात;捌;ஒன்பது Do digitsinit ; Initialize data for conversion between integers and strings ; Get number of CPUs from /proc/cpuinfo and calculate minimum number of execution streams Open "cpus":(SHELL="/bin/sh":COMMAND="grep -i ^processor /proc/cpuinfo|wc -l":READONLY)::"PIPE" Use "cpus" Read streams Use $PRINCIPAL Close "cpus" Set streams=2*streams ; At least two execution streams per CPU ; At the top level, the program reads and processes input lines, one at a time. Each line specifies ; one problem to solve. Since the program is designed to resume after a crash and reuse partial ; results computed before the crash, data in the database at the beginning is assumed to be partial ; results from the previous run. After computing and writing results for a line, the database is ; cleared for next line of input or next run of the program. ; Loop for ever, read a line (quit on end of file), process that line For Read input Quit:$ZEOF!'$Length(input) Do ; input has entire input line . . Set i=$Piece(input," ",1) ; i - first number on line is starting integer for the problem . Set j=$Piece(input," ",2) ; j - second number on line is ending integer for the problem . Write $FNumber(i,",",0)," ",$FNumber(j,",",0) ; print starting and ending integers, formatting with commas . . Set k=$Piece(input," ",3) ; k - third number on input line is number of parallel streams . If streams>k Do ; print number of execution streams, optionally corrected .. Write " (",$FNumber(k,",",0) .. Set k=streams .. Write "->",$FNumber(k,",",0),")" . Else Write " ",$FNumber(k,",",0) . . Set blk=+$Piece(input," ",4) ; blk - size of blocks of integers is optional fourth piece . Set tmp=(j-i+k)\k ; default / maximum block size . If blk&(blk'>tmp) Write " ",$FNumber(blk,",",0) ; print block size, optionally corrected . Else Do .. Write " (",$FNumber(blk,",",0) .. Set blk=tmp .. Write "->",$FNumber(blk,",",0),")" . . ; Define blocks of integers for child processes to work on . Kill ^limits . Set tmp=i-1 . For count=1:1 Quit:tmp=j Do .. Set ^limits(count)=$increment(tmp,blk) .. Set:tmp>j (tmp,^limits(count))=j . . ; Launch jobs. Grab lock l1, atomically increment counter, compute and launch one job for each block of numbers. . ; Each child job locks l2(pid), decrements the counter and tries to grab lock l1(pid). . ; When counter is zero, all jobs have started. Parent releases lock l1 and tries to grab lock l2. . ; When all children have released their l2(pid) locks, they're done and parent can gather & report results. . Set ^count=0 ; Clear ^count - may have residual value if restarting from crash . Lock +l1 ; Set lock for process synchronization . For s=1:1:k Do .. Set c=$Increment(^count) ; Atomic increment of counter in database for process synchronization .. Set def=$ZTRNLNM("gtm_tmp") Set:'$Length(def) def=$ZTRNLNM("PWD") ; Working directory for Jobbed process .. Set err=$Text(+0)_"_"_$Job_"_"_s_".mje" ; STDERR for Jobbed process .. Set out=$Extract(err,1,$Length(err)-1)_"o" ; STDOUT for Jobbed process .. Set cmd="doblk(i):(ERROR="""_err_""":OUTPUT="""_out_""":DEFAULT="""_def_""")" ; Command to Job .. Job @cmd ; Job child process for next block of numbers . For Quit:'^count Hang 0.1 ; Wait for processes to start (^count goes to 0 when they do) . Lock -l1 ; Release lock so processes can run . Set startat=$HOROLOG ; Get starting time . Lock +l2 ; Wait for processes to finish . . ; When parent gets lock l2, child processes have completed and parent gathers and reports results. . set endat=$HOROLOG ; Get ending time - time between startat and endat is the elapsed time . ; Calculate duration . Set duration=(86400*($Piece(endat,",",1)-$Piece(startat,",",1)))+$Piece(endat,",",2)-$Piece(startat,",",2) . Write " ",$FNumber(^result,",",0) ; Show largest number of steps for the range i through j . Write " ",$FNumber(^highest,",",0) ; Show the highest number reached during the computation . Write " ",$FNumber(duration,",",0) ; Show the elapsed time . Write " ",$FNumber(^updates,",",0) ; Show number of updates . Write " ",$FNumber(^reads,",",0) ; Show number of reads . ; If duratation is greater than 0 seconds, display update and read rates . Write:duration " ",$FNumber(^updates/duration,",",0)," ",$FNumber(^reads/duration,",",0) . Write ! . Lock -l2 ; Release lock for next run . Do dbinit ; Initialize database for next run Quit dbinit ; Entryref dbinit clears database between lines Kill ^count,^highest,^reads,^result,^step,^updates Quit digitsinit ; Initialize arrays to convert between strings and integers New m,x Set x=$Text(digits) For m=0:1:9 Set di($Piece(x,";",m+2))=m,ds(m)=$Piece(x,";",m+2) Quit inttostr(n) ; Convert an integer to a string New m,s Set s=ds($Extract(n,1)) For m=2:1:$Length(n) Set s=s_" "_ds($Extract(n,m)) Quit s ; strtoint(s) ; Convert a string to an integer New m,n Set n=di($Piece(s," ",1)) For m=2:1:$Length(s," ") Set n=10*n+di($Piece(s," ",m)) Quit n ; This is where Jobbed processes start doblk(allfirst) Set (reads,updates,highest)=0 ; Start with zero reads, writes and highest number Do digitsinit ; Initialize data for conversion between integers and strings Lock +l2($JOB) ; Get lock l2 that parent will wait on till this Jobbed processes is done If $Increment(^count,-1) ; Decrement ^count to say this process is alive Lock +l1($JOB) ; This process will get lock l1($JOB) only parent has released lock on l1 ; ; Process the next block in ^limits that needs processing; quit when done For Quit:'$Data(^limits($increment(tmp))) Do:1=$increment(^limits(tmp,1)) dostep($select($data(^limits(tmp-1)):^limits(tmp-1)+1,1:allfirst),^limits(tmp)) ; TStart ; Update global statistics inside a transaction ; The following line unconditionally adds the number of reads & write performed by this process to the ; number of reads & writes performed by all processes, and sets the highest for all processes if the ; highest calculated by this process is greater than that calculated so far for all processes Set:$Increment(^reads,reads)&$Increment(^updates,updates)&(highest>$Get(^highest)) ^highest=highest TCommit Lock -l1($JOB),-l2($JOB) ; Release locks to tell parent this parent is done Quit ; Jobbed processes terminate here dostep(first,last) ; Calculate the maximum number of steps from first through last New current,currpath,i,n For current=first:1:last Do . Set n=current ; Start n at current . Kill currpath ; Currpath holds path to 1 for current . ; Go till we reach 1 or a number with a known number of steps . For i=0:1 Quit:$Increment(reads)&($Data(^step($$inttostr(n)))!(1=n)) Do .. Set currpath(i)=n ; log n as current number in sequence .. Set n=$Select('(n#2):n/2,1:3*n+1) ; compute the next number .. Set:n>highest highest=n ; see if we have a new highest number reached . Do:0$Get(^result) ^result=i .. TCommit .. Set n="" For Set n=$Order(currpath(n)) Quit:""=n Set:$Increment(updates) ^step($$inttostr(currpath(n)))=$$inttostr(i-n) Quit

The following code is a complete implementation of ROT13, a trivially breakable cipher used for various purposes on the Net, not high security. It illustrates the compact nature of MUMPS code and is rather less cryptic than the sample above.

ST ; ROT13 ; Gunter Rensch ; 2000-01-03 ; Encrypt/Decrypt ROT13 Q ; no direct execution ; ; call from your program with ; S A="String" ; S A=$$ROT^ROT13(.A) ; ROT(R) ; S S1="ABCDEFGHIJKLMNOPQRSTUVWXYZ" S S2="NOPQRSTUVWXYZABCDEFGHIJKLM" S s1="abcdefghijklmnopqrstuvwxyz" S s2="nopqrstuvwxyzabcdefghijklm" S R=$TR(R,S1_s1,S2_s2) Q R

A second implementation is below, which illustrates the possibilities of concision in MUMPS.

s A="String" F i=1:1:$L(A) W $c($S($A($E(A,i))<91:$A($E(A,i))-52#26+65,1:$A($E(A,i))-84#26+97))

Finally, one of the shortest programs ever written in a high-level language, demonstrating the extreme concision of which MUMPS is capable.

s x="x x" x x

The same algorithm using expanded variable and command names

Set X="Xecute X" Xecute X

This program sets a value of "x x" to a variable named x, and then launches an infinite recursive execution of x, probably resulting in a stack overflow. At just 13 characters, including spaces and an end-of-line mark (since the MUMPS standard specifies storage in characters, not in bytes), using just two characters, the first variant demonstrates that it is also possible to write obscure and obfuscated code in M.