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问题:

以最有效的方式逐行读取*平台专用*

姚嘉容
2023-03-14

代码将是特定于平台的windows OS

与事实,我正在写一个特定的当前CPU等'…

*别介意它不是多平台的。

typdef struct _FileL{
 uint lidx;
 char* lncontent;
} FileL;
getFileLines(char* fullPath, FileL** fileLines){
    uint linesCount = 0;// total lines
    uint curLnIndex = 0;// lines counter

    FILE* srcFL; // will hold the source file using passed fullPath

    // now read file into memory 
    //that is the only way i could think of 
    //to be able to assign lineCount used to calculate the array length
    //and also the fastest way is  to read the whole file into memory (?)

    srcFL = fopen(fullPath,"r"); // or open() instead of fopen() ?

   // problem:
   // assigning lineCount somehow would cost the time of reading
   // and might aswell just populate it and already store to array..
   // so what is the workaround ?

  *fileLines =(FileL*) malloc (linesCount * sizeof(FileL));
   FileL* CurLn = *fileLines;

   while(curLnIndex != linesCount){
     char* TmpLnCont;
     //read line into TmpLnCont..
     CurLn->lidx = curLnIndex ;
     CurLn->lncontent = (char*)malloc(sizeof(TmpLnCont));
     strcpy(CurLn->lncontent, TmpLnCont);
   }
}

怎样才是更有效的方法?

编辑:

我想更新这个问题,因为我想解决效率问题:最有效的方法可以追溯到每行扫描文件的细节,是否是逐个字符的唯一方法,如何避免在每个字符上调用函数...任何可以最大限度地提高每行循环性能的东西,这意味着有效地获得一行的定义...

共有1个答案

漆雕原
2023-03-14

执行读取(2)不是很好,因为行的碎片(例如,如果读取1000个字符,最后一行可能从偏移量990开始,需要超出缓冲区50个字符)。

最好使用fgets[推荐]或mmap[YMMV]。以下是每种方法的例子。警告:编译,但没有测试,也不做很多错误检查

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/mman.h>

typedef struct {
    unsigned int lidx;
    char *lncontent;
} FileL;

// read in file lines using fgets
FileL *
getfileline_fgets(char *file)
{
    FILE *xf;
    char *cp;
    int len;
    int linecnt;
    int linemax;
    FileL *linelist;
    FileL *line;
    char lbuf[50000];

    xf = fopen(file,"r");

    linecnt = 0;
    linemax = 0;
    linelist = NULL;

    while (1) {
        cp = fgets(lbuf,sizeof(lbuf),xf);
        if (cp == NULL)
            break;

        len = strlen(lbuf);

        // strip newline from string [or not]
#if 1
        if (len > 0) {
            cp = &lbuf[len - 1];
            if (*cp == '\n') {
                *cp = 0;
                --len;
            }
        }
#endif

        if ((linecnt + 1) > linemax) {
            linemax += 100;
            linelist = realloc(linelist,linemax * sizeof(FileL));
        }

        line = &linelist[linecnt];
        line->lidx = linecnt++;

        cp = malloc(len + 1);
        memcpy(cp,lbuf,len + 1);
        line->lncontent = cp;
    }

    fclose(xf);

    // trim to maximum used
    linelist = realloc(linelist,linecnt * sizeof(FileL));

    return linelist;
}

// read in file lines by mmap to entire file
FileL *
getfilelines_mmap(char *file)
{
    int fd;
    char *lhs;
    char *rhs;
    char *cp;
    int len;
    int linecnt;
    int linemax;
    FileL *linelist;
    FileL *line;
    struct stat st;
    char *fbuf;
    char cbuf[50000];

    fd = open(file,O_RDONLY);
    fstat(fd,&st);

    fbuf = mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,fd,0);

    linecnt = 0;
    linemax = 0;
    linelist = NULL;

    lhs = fbuf;
    rhs = fbuf;

    for (lhs = fbuf;  lhs < &fbuf[st.st_size];  lhs = rhs + 1) {
        rhs = strchr(lhs,'\n');

        // NOTE: does _not_ handle case of malformed text file that has _no_
        // newline on last line
        if (rhs == NULL)
            break;

        len = rhs - lhs;

        // strip newline from string [or not]
#if 1
        if (len > 0)
            --len;
#endif

        if ((linecnt + 1) > linemax) {
            linemax += 100;
            linelist = realloc(linelist,linemax * sizeof(FileL));
        }

        line = &linelist[linecnt];
        line->lidx = linecnt++;

        cp = malloc(len + 1);
        memcpy(cp,lhs,len);
        cp[len] = 0;
        line->lncontent = cp;
    }

    munmap(fbuf,st.st_size);
    close(fd);

    // trim to maximum used
    linelist = realloc(linelist,linecnt * sizeof(FileL));

    return linelist;
}

更新

23:39:35.528333425 NEWDAY 11/09/15
23:39:35.528333425 ph: starting 23107 ...
23:39:35.528868198 ph: ARGV fastreadgo ...

F001: L:324255 W:2097 324.086MB
    368297556 fgets
    189180143 mmap

F002: L:329608 W:2822 443.649MB
    475989122 fgets
    248517335 mmap

F003: L:401476 W:6186 1185.270MB
   1206999411 fgets
    657703847 mmap

F004: L:729379 W:9350 3253.185MB
   3199692871 fgets
   1776602082 mmap

F005: L:85857 W:5185 212.599MB
    223489564 fgets
    122404608 mmap

F006: L:62871 W:5418 162.384MB
    167640768 fgets
     93127042 mmap

F007: L:298836 W:1083 154.481MB
    196584474 fgets
    100582134 mmap

F008: L:221513 W:2732 288.694MB
    322105867 fgets
    164965547 mmap

F009: L:420815 W:8906 1789.672MB
   1801309998 fgets
    961136893 mmap

F010: L:126712 W:8251 498.905MB
    499274233 fgets
    275901635 mmap

F011: L:443166 W:8822 1865.753MB
   1839816883 fgets
   1001882651 mmap

F012: L:385632 W:2162 398.467MB
    467223648 fgets
    248126909 mmap

F013: L:629448 W:4413 1324.616MB
   1432284339 fgets
    777593198 mmap

F014: L:510357 W:7313 1779.348MB
   1919309671 fgets
   1079111734 mmap

F015: L:188434 W:1254 112.922MB
    152367682 fgets
     78959769 mmap

F016: L:82139 W:4355 170.586MB
    193117015 fgets
    105417805 mmap

F017: L:389499 W:9063 1681.805MB
   1730894028 fgets
    913789253 mmap

F018: L:992849 W:3265 1547.875MB
   1685006767 fgets
    875256226 mmap

F019: L:931502 W:9647 4285.883MB
  11181005402 fgets
   2361255543 mmap

F020: L:266047 W:7454 946.298MB
    955772708 fgets
    537059554 mmap

F021: L:572709 W:67 18.835MB
     86539501 fgets
     43437303 mmap

F022: L:68373 W:3042 98.684MB
    110325296 fgets
     57538963 mmap

F023: L:651839 W:2006 624.153MB
    706094723 fgets
    369122560 mmap

F024: L:414658 W:6482 1284.202MB
   1294352248 fgets
    700279769 mmap

F025: L:984554 W:3441 1616.269MB
   1742233370 fgets
    903755131 mmap

F026: L:527629 W:3214 808.812MB
    872660092 fgets
    465403685 mmap

F027: L:572103 W:6219 1696.582MB
   1758562312 fgets
    933024466 mmap

F028: L:793354 W:5967 2255.653MB
   2341754885 fgets
   1251633414 mmap

F029: L:690669 W:389 128.888MB
    230036016 fgets
    119381427 mmap

F030: L:902519 W:8182 3523.415MB
   6665490426 fgets
   1930049511 mmap

F031: L:179482 W:2361 201.850MB
    225333697 fgets
    120424715 mmap

F032: L:342396 W:4135 675.885MB
    706219203 fgets
    379974402 mmap

F033: L:762237 W:4000 1455.780MB
   1535236381 fgets
    805977762 mmap

F034: L:421947 W:8289 1669.038MB
   1686877811 fgets
    900813641 mmap

F035: L:367349 W:5829 1022.373MB
   1051584165 fgets
    566680706 mmap

F036: L:433973 W:5064 1049.724MB
   1097920811 fgets
    584855289 mmap

F037: L:615918 W:9152 2686.372MB
   2743719787 fgets
   1468536802 mmap

F038: L:365187 W:1564 272.829MB
    326368364 fgets
    171071840 mmap

F039: L:61305 W:477 14.002MB
     22945438 fgets
     11949833 mmap

F040: L:396788 W:8576 1622.049MB
   1633217001 fgets
    884460205 mmap

F041: L:245326 W:5068 592.450MB
    610530077 fgets
    328366102 mmap

F042: L:986409 W:9174 4313.608MB
  17048484450 fgets
   2413375121 mmap

F043: L:367968 W:9703 1703.785MB
   1677764299 fgets
    922735827 mmap

F044: L:630679 W:9763 2942.911MB
   4742195305 fgets
   1585438052 mmap

F045: L:397072 W:7717 1459.554MB
   1533634531 fgets
    860518182 mmap

F046: L:918129 W:9127 3996.179MB
  10259712214 fgets
   2171550789 mmap

F047: L:770706 W:2720 999.584MB
   1097599308 fgets
    604894013 mmap

F048: L:472462 W:5011 1127.896MB
   1164186449 fgets
    621979909 mmap

F049: L:301834 W:4456 642.703MB
    664420452 fgets
    354255131 mmap

F050: L:213878 W:2913 297.159MB
    321396955 fgets
    168664579 mmap

F051: L:549950 W:1681 441.842MB
    510553173 fgets
    260455948 mmap

F052: L:63502 W:8785 267.074MB
    265697002 fgets
    142457939 mmap

F053: L:880396 W:6821 2864.595MB
   3769485430 fgets
   1591318886 mmap

F054: L:180543 W:9055 779.566MB
    773462618 fgets
    428627500 mmap

F055: L:964409 W:8454 3884.437MB
   9085108760 fgets
   2149540695 mmap

F056: L:675120 W:8912 2872.781MB
   2885159527 fgets
   1559580604 mmap

F057: L:345151 W:4157 684.052MB
    724456228 fgets
    387170980 mmap

F058: L:69114 W:4585 150.535MB
    157447952 fgets
     84782951 mmap

F059: L:304627 W:9441 1370.777MB
   1376517664 fgets
    739170571 mmap

F060: L:799770 W:3145 1200.762MB
   1304001986 fgets
    679163462 mmap

F061: L:808699 W:6544 2523.949MB
   2590924710 fgets
   1385627164 mmap

F062: L:270082 W:313 40.592MB
     78777863 fgets
     40733146 mmap

F063: L:308883 W:333 49.262MB
     93696361 fgets
     48580067 mmap

F064: L:237002 W:2618 296.446MB
    347315129 fgets
    178078149 mmap

F065: L:279040 W:1341 178.685MB
    217230537 fgets
    113291912 mmap

F066: L:809386 W:2808 1085.734MB
   1177480987 fgets
    615248653 mmap

F067: L:279448 W:8560 1140.280MB
   1151044788 fgets
    614662533 mmap

F068: L:80012 W:7441 283.334MB
    286915203 fgets
    158077955 mmap

F069: L:366808 W:7197 1260.521MB
   1292679736 fgets
    696686301 mmap

F070: L:272693 W:9275 1206.527MB
   1220763889 fgets
    658383413 mmap

F071: L:792609 W:1419 537.088MB
    645760162 fgets
    334886975 mmap

F072: L:742523 W:8640 3059.604MB
   5711688133 fgets
   1665879727 mmap

F073: L:583753 W:2992 833.759MB
    910037328 fgets
    483847376 mmap

F074: L:252560 W:7178 864.593MB
    868625985 fgets
    471770777 mmap

F075: L:154327 W:7026 515.619MB
    516135586 fgets
    277690063 mmap

F076: L:121839 W:7131 414.684MB
    424518600 fgets
    230518357 mmap

F077: L:760327 W:1421 515.475MB
    622630358 fgets
    314592959 mmap

F078: L:907033 W:3485 1508.042MB
   1622356297 fgets
    845695719 mmap

F079: L:884787 W:7491 3162.774MB
   4932864122 fgets
   1749065509 mmap

F080: L:432556 W:6039 1245.779MB
   1281231973 fgets
    693532807 mmap

F081: L:639804 W:6419 1957.747MB
   2107303517 fgets
   1130299002 mmap

F082: L:388669 W:283 52.804MB
    111686630 fgets
     57177517 mmap

F083: L:300542 W:1943 278.825MB
    336538347 fgets
    177494803 mmap

F084: L:941 W:7,3878 1.770MB
      2047540 fgets
      1347230 mmap

F085: L:85747 W:1841 75.417MB
     92274672 fgets
     49362653 mmap

F086: L:935559 W:5950 2656.411MB
   2734326131 fgets
   1487147776 mmap

F087: L:936993 W:1197 535.727MB
    672872562 fgets
    348765250 mmap

F088: L:409671 W:5235 1023.358MB
   1099320520 fgets
    606047909 mmap

F089: L:362220 W:5434 938.805MB
    991448256 fgets
    529093412 mmap

F090: L:628156 W:3682 1103.909MB
   1185317812 fgets
    637902310 mmap

F091: L:655456 W:6051 1892.574MB
   1978859918 fgets
   1066368241 mmap

F092: L:356309 W:5946 1012.893MB
   1046818030 fgets
    562463577 mmap

F093: L:878726 W:2946 1236.162MB
   1368885560 fgets
    701514499 mmap

F094: L:583863 W:747 208.701MB
    293177923 fgets
    148045230 mmap

F095: L:51374 W:3752 91.670MB
     98830853 fgets
     52715699 mmap

F096: L:757271 W:4698 1698.664MB
   1790811621 fgets
    946452098 mmap

F097: L:665420 W:1814 575.369MB
    664290848 fgets
    347346293 mmap

F098: L:152806 W:4480 326.336MB
    338683910 fgets
    185037896 mmap

F099: L:39027 W:2368 44.104MB
     49144948 fgets
     26701307 mmap

F100: L:896926 W:8209 3513.328MB
   7460727008 fgets
   1900543480 mmap

F101: L:796628 W:5663 2149.888MB
   2207899454 fgets
   1187397751 mmap

F102: L:876500 W:1986 831.161MB
    934850175 fgets
    486626065 mmap

F103: L:188682 W:773 69.722MB
     97285527 fgets
     48765985 mmap

F104: L:648920 W:9590 2969.446MB
   5021968784 fgets
   1622268239 mmap

F105: L:827850 W:2123 837.892MB
    946063144 fgets
    498163978 mmap

F106: L:879828 W:2867 1205.021MB
   1304295176 fgets
    682155187 mmap

F107: L:970674 W:3830 1771.667MB
   1883664162 fgets
    989569477 mmap

F108: L:4461 W:5634 11.840MB
     12680659 fgets
      7159011 mmap

F109: L:477207 W:1067 243.224MB
    315370392 fgets
    162708299 mmap

F110: L:140308 W:5817 389.132MB
    397510757 fgets
    216204659 mmap

F111: L:253358 W:4425 534.937MB
    559943651 fgets
    297109524 mmap

F112: L:903292 W:7989 3441.851MB
   7327033977 fgets
   1906200470 mmap

F113: L:555989 W:620 164.835MB
    245638038 fgets
    126559933 mmap

F114: L:596425 W:2330 664.143MB
    739017073 fgets
    391237002 mmap

F115: L:298147 W:9741 1387.530MB
   1363229979 fgets
    744420477 mmap

F116: L:180269 W:4522 389.175MB
    402702977 fgets
    213875684 mmap

F117: L:238597 W:9021 1029.314MB
   1033070395 fgets
    550442036 mmap

F118: L:183723 W:8705 764.555MB
    765959712 fgets
    413667801 mmap

F119: L:174802 W:549 45.896MB
     70635625 fgets
     35721310 mmap

F120: L:883013 W:4666 1963.677MB
   2062197751 fgets
   1092583730 mmap

F121: L:858995 W:9218 3776.896MB
   9278222413 fgets
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F122: L:368895 W:5862 1030.174MB
   1076473726 fgets
    582127460 mmap

F123: L:208043 W:5672 563.889MB
    579427255 fgets
    310321934 mmap

F124: L:768482 W:4953 1816.657MB
   1888233155 fgets
    997797932 mmap

F125: L:905425 W:2812 1214.882MB
   1394928053 fgets
    724059403 mmap

F126: L:54137 W:4690 121.066MB
    125124760 fgets
     67811537 mmap

F127: L:448100 W:9643 2061.624MB
   2066282543 fgets
   1126488038 mmap

F128: L:748979 W:2111 754.038MB
    854095589 fgets
    447406977 mmap

F129: L:611388 W:6954 2026.306MB
   2074219917 fgets
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F130: L:782834 W:9946 3715.067MB
   7338500374 fgets
   2029571615 mmap

F131: L:52630 W:7858 197.495MB
    200711062 fgets
    110759659 mmap

F132: L:930983 W:7363 3270.546MB
   3376813502 fgets
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F133: L:73216 W:2127 74.344MB
     85854537 fgets
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F134: L:583306 W:2495 694.192MB
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F135: L:877424 W:2964 1241.342MB
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F136: L:414854 W:5104 1010.006MB
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F137: L:333176 W:4912 781.109MB
    820007572 fgets
    435433956 mmap

F138: L:564006 W:6933 1863.574MB
   1905024687 fgets
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F139: L:829571 W:9152 3622.399MB
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F140: L:560210 W:7443 1990.047MB
   2012670010 fgets
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00:00:58.770988225 NEWDAY 11/10/15
00:00:58.770988225 ph: complete (ELAPSED: 00:21:23.190149545)
#!/usr/bin/perl
# grpcntgen -- generate test data for fastread algorithms
#
# arguments:
#   "-W" - maximum line width
#   "-L" - maximum number of lines
#   "-T" - number of test files to generate
#   "-O" - output file (e.g. foo%.txt)
#
# NOTE: with no arguments or missing arguments will prompt

#pragma pgmlns
# tstgen -- test generation help routines

# gengetstr -- get a string/number
sub gengetstr
{
    my($numflg,$opt,$prompt,$lim) = @_;
    my($arg);
    my($askflg);
    my($val);

    select(STDOUT);
    $| = 1;

    {
        # search command line for -whatever
        foreach $arg (@argv) {
            if ($arg =~ /^$opt(.*)$/) {
                $val = $1;
                if ($numflg && ($val eq "")) {
                    $val = $lim;
                    $val //= 1;
                }
                last;
            }
        }
        last if (defined($val));

        $askflg = 1;

        while (1) {
            printf("Enter ")
                if ($numflg != 1);

            printf("%s",$prompt);

            if ($numflg == 1) {
                printf(" (0/1)? ");
            }
            else {
                printf(": ");
            }

            $val = <STDIN>;
            chomp($val);

            if ($numflg == 0) {
                last if ($val ne "");
                next;
            }

            # an empty response for a number with a maximum means use it
            if (($numflg == 2) && ($val eq "") && defined($lim)) {
                $val = $lim;
                last;
            }

            next unless ($val =~ /^\d+$/);

            $val += 0;

            last if ($numflg == 1);

            next if ($val <= 0);
            last unless (defined($lim));
            last if ($val <= $lim);
        }
    }

    unless ($askflg) {
        printf("%s: %s\n",$prompt,$val);
    }

    $val;
}

# genrun -- generate all tests
sub genrun
{
    local(@argv) = @_;
    local($ofile,$tstmax,$tstproc);
    local($tstcur);
    local($splitflg);
    local($genvbq);
    my($sym);
    my($numfmt);
    my($xfile);

    $genvbq = genvbq(\@argv);

    $ofile = shift(@argv);
    $tstmax = shift(@argv);
    $tstproc = shift(@argv);

    # split each test into separate file
    if ($ofile =~ /%/) {
        $splitflg = 1;
        $numfmt = sprintf("%d",$tstmax);
        $numfmt = length($numfmt);
        $numfmt = sprintf("_%%%d.%dd",$numfmt,$numfmt);
        $ofile =~ s/%/$numfmt/;
        ###die("genrun: DEBUG_CAE numfmt='$numfmt' ofile='$ofile'\n");
    }

    {
        last if ($splitflg);
        genopen($ofile);
    }

    for ($tstcur = 1;  $tstcur <= $tstmax;  ++$tstcur) {
        {
            last unless ($splitflg);
            $xfile = sprintf($ofile,$tstcur);
            genopen($xfile);
        }

        &$tstproc();

        {
            last unless ($splitflg);
            genclose();
        }
    }

    {
        last if ($splitflg);
        genclose();
    }
}

# genvbq -- get options
sub genvbq
{
    my($argv) = @_;
    my($sym);
    my($env);

    $env = {};

    while (1) {
        $sym = $argv->[0];
        last unless ($sym =~ s/^-//);
        shift(@$argv);

        if ($sym =~ /^([^=]+)=(.+)$/) {
            ($sym,$val) = ($1,$2);
        }
        else {
            $val = 1;
        }

        $env->{$sym} = $val;
    }

    $env;
}

# genopen -- open output
sub genopen
{
    my($ofile) = @_;

    $gen_ofile = $ofile;

    {
        last if ($genvbq->{"n"});
        last if (open($xfdst,">$ofile"));
        die("genopen: unable to open '$ofile' -- $!\n");
    }
}

# genclose -- close output
sub genclose
{

    close($xfdst);
}

# geninit -- initialize for single test
sub geninit
{

    undef($genout_lhs);
    undef($genout_pre);
}

# genout -- output data
sub genout
{
    my($rhs) = @_;

    {
        if (defined($rhs)) {
            last if ((length($genout_pre) + length($genout_lhs) +
                length($rhs)) < 78);
        }

        last if ($genout_lhs eq "");

        print($xfdst $genout_pre,$genout_lhs,"\n");
        undef($genout_lhs);
    }

    $genout_lhs .= $rhs
        if (defined($rhs));
}

# genrand -- get random number
sub genrand
{
    my($lim) = @_;
    my($val);

    $val = int(rand($lim));
    $val += 1;

    $val;
}

# genfmtof -- get number format
sub genfmtof
{
    my($num) = @_;
    my($fmt);

    $fmt = sprintf("%d",$num);
    $fmt = length($fmt);
    $fmt = sprintf(" %%%dd",$fmt);

    $fmt;
}

1;

master(@ARGV);
exit(0);

# master -- master control
sub master
{
    local(@argv) = @_;

    $Wmax = gengetstr(2,"-W","maximum line width");
    $Lmax = gengetstr(2,"-L","maximum number of lines / file");
    $tstmax = gengetstr(2,"-T","number of tests");

    while (1) {
        $ofile = gengetstr(0,"-O","output file name");
        last if ($ofile =~ /%/);
        printf("fastreadgen: filename must have %% in it (e.g. foo%%.txt)\n");
    }

    genrun($ofile,$tstmax,\&dotest);
}

# dotest -- generate a test
sub dotest
{
    my($lno,$chroff);
    my($lhs);

    $Wlim = genrand($Wmax);
    $Llim = genrand($Lmax);

    printf("dotest: T=%d/%d W=%d L=%d\n",$tstcur,$tstmax,$Wlim,$Llim);

    for ($lno = 1;  $lno <= $Llim;  ++$lno) {
        $Wcur = genrand($Wlim);
        $Wcur -= 1;

        undef($lhs);
        for (;  $Wcur > 0;  --$Wcur) {
            $chroff = genrand(0x7E - 0x20);
            $chroff += 0x20;
            $chroff -= 1;
            $chroff = chr($chroff);
            last;
            $lhs .= $chroff;
        }
        $lhs = $chroff x $Wcur;

        print($xfdst $lhs,"\n");
    }
}
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