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What kind of overhead is involved in a Hashtable?


What kind of overhead is involved in a Hashtable?

By : TechnoWizard
Date : October 15 2020, 11:12 PM
around this issue Theoretically, it depends on how many unique numbers there are in the stream of numbers. But any real life scenario I can imagine, an array would be ridiculously slower. The more unique numbers you process, the slower the array solution will become.
A HashTable generally maintains the same access speed no matter how large it becomes. For an 'infinite stream', I can't imagine how a HashTable won't be the better solution. How do you intend to search the array?
code :


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Is there much overhead involved in VBA classes?

Is there much overhead involved in VBA classes?


By : user1573959
Date : March 29 2020, 07:55 AM
To fix the issue you can do To answer your question, there is a little overhead with classes. Namely the creation and destruction of those objects. Also accessing properties can be a wee bit slower. But generally speaking, it should be a fairly negligible amount. You really shouldn't see any difference at all unless you measuring in milliseconds. A more likely culperit is the way the code is now structured. I would advise stepping through the code and observing what it is actually doing. It could be possible there are things you can do to optimize the code.
To give an example: If you have a property that performs a look-up on a value that won't have changed consider having the first access of that property lookup up the value and store it for future reference. So any calls to that property thereafter don't have to perform the lookup. If you think the data may change, consider using a refresh method, or an optional refresh parameter.
Overhead involved in nested sequences in F#

Overhead involved in nested sequences in F#


By : ray
Date : March 29 2020, 07:55 AM
wish of those help I thought the call to Seq.collect might cause it to generate an IEnumerable per call, so I replaced it with a for loop and it produces the same output (via ILSpy).
That made me curious so I decompiled a simpler sequence expression I'd expect to be "flattened."
code :
let rec infSeq n =
  seq {
    yield n
    yield! infSeq (n+1)
  }
public override int GenerateNext(ref IEnumerable<int> next)
{
    switch (this.pc)
    {
    case 1:
        this.pc = 2;
        next = Test.infSeq(this.n + 1);
        return 2;
    case 2:
        this.pc = 3;
        break;
    case 3:
        break;
    default:
        this.pc = 1;
        this.current = this.n;
        return 1;
    }
    this.current = 0;
    return 0;
}
infSeq 0 |> Seq.take 10000000 |> Seq.length
> Real: 00:00:01.759, CPU: 00:00:01.762, GC gen0: 108, gen1: 107, gen2: 1
public static IEnumerable<int> InfSeq(int n) {
    while (true) yield return n++;
}
> Real: 00:00:00.991, CPU: 00:00:00.998, GC gen0: 0, gen1: 0, gen2: 0
When catching SIGSEGV from within, how to known the kind of invalid access involved?

When catching SIGSEGV from within, how to known the kind of invalid access involved?


By : AshèCode
Date : March 29 2020, 07:55 AM
This might help you It turns out that in Linux on x86-64 (aka AMD64) architecture, this is in fact quite feasible.
Here is an example program, crasher.c:
code :
#define  _POSIX_C_SOURCE 200809L
#define  _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <ucontext.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>

#if !defined(__linux__) || !defined(__x86_64__)
#error This example only works in Linux on x86-64.
#endif

#define  ALTSTACK_SIZE  262144

static const char hex_digit[16] = {
    '0', '1', '2', '3', '4', '5', '6', '7',
    '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
};

static inline const char *signal_name(const int signum)
{
    switch (signum) {
    case SIGSEGV: return "SIGSEGV";
    case SIGBUS:  return "SIGBUS";
    case SIGILL:  return "SIGILL";
    case SIGFPE:  return "SIGFPE";
    case SIGTRAP: return "SIGTRAP";
    default:      return "(unknown)";
    }
}

static inline ssize_t internal_write(int fd, const void *buf, size_t len)
{
    ssize_t retval;
    asm volatile ( "syscall\n\t"
                 : "=a" (retval)
                 : "a" (1), "D" (fd), "S" (buf), "d" (len)
                 : "rcx", "r11" );
    return retval;
}

static inline int wrerr(const char *p, const char *q)
{
    while (p < q) {
        ssize_t n = internal_write(STDERR_FILENO, p, (size_t)(q - p));
        if (n > 0)
            p += n;
        else
        if (n == 0)
            return EIO;
        else
            return -n;
    }
    return 0;
}

static inline int wrs(const char *p)
{
    if (p) {
        const char *q = p;
        while (*q)
            q++;
        return wrerr(p, q);
    }
    return 0;
}

static inline int wrh(unsigned long h)
{
    static char buffer[4 + 2 * sizeof h];
    char       *p = buffer + sizeof buffer;

    do {
        *(--p) = hex_digit[h & 15];
        h /= 16UL;
    } while (h);

    *(--p) = 'x';
    *(--p) = '0';

    return wrerr(p, buffer + sizeof buffer);
}

static void crash_handler(int signum, siginfo_t *info, void *contextptr)
{
    if (info) {
        ucontext_t *const ctx = (ucontext_t *const)contextptr;
        wrs(signal_name(signum));
        if (ctx->uc_mcontext.gregs[REG_ERR] & 16) {
            const unsigned long sp = ctx->uc_mcontext.gregs[REG_RSP];
            /* Instruction fetch */
            wrs(": Bad jump to ");
            wrh((unsigned long)(info->si_addr));
            if (sp && !(sp & 7)) {
                wrs(" probably by the instruction just before ");
                wrh(*(unsigned long *)sp);
            }
            wrs(".\n");
        } else
        if (ctx->uc_mcontext.gregs[REG_ERR] & 2) {
            /* Write access */
            wrs(": Invalid write attempt to ");
            wrh((unsigned long)(info->si_addr));
            wrs(" by instruction at ");
            wrh(ctx->uc_mcontext.gregs[REG_RIP]);
            wrs(".\n");
        } else {
            /* Read access */
            wrs(": Invalid read attempt from ");
            wrh((unsigned long)(info->si_addr));
            wrs(" by instruction at ");
            wrh(ctx->uc_mcontext.gregs[REG_RIP]);
            wrs(".\n");
        }
    }

    raise(SIGKILL);
}

static int install_crash_handler(void)
{
    stack_t           altstack;
    struct sigaction  act;

    altstack.ss_size = ALTSTACK_SIZE;
    altstack.ss_flags = 0;
    altstack.ss_sp = mmap(NULL, altstack.ss_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_GROWSDOWN, -1, 0);
    if (altstack.ss_sp == MAP_FAILED) {
        const int retval = errno;
        fprintf(stderr, "Cannot map memory for alternate stack: %s.\n", strerror(retval));
        return retval;
    }
    if (sigaltstack(&altstack, NULL)) {
        const int retval = errno;
        fprintf(stderr, "Cannot use alternate signal stack: %s.\n", strerror(retval));
        return retval;
    }

    memset(&act, 0, sizeof act);
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_SIGINFO | SA_ONSTACK;
    act.sa_sigaction = crash_handler;
    if (sigaction(SIGSEGV, &act, NULL) == -1 ||
        sigaction(SIGBUS,  &act, NULL) == -1 ||
        sigaction(SIGILL,  &act, NULL) == -1 ||
        sigaction(SIGFPE,  &act, NULL) == -1) {
        const int retval = errno;
        fprintf(stderr, "Cannot install crash signal handlers: %s.\n", strerror(retval));
        return retval;
    }

    return 0;
}

int main(int argc, char *argv[])
{
    void         (*jump)(void) = 0;
    unsigned char *addr = (unsigned char *)0;

    if (argc < 2 || argc > 3 || !strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
        fprintf(stderr, "\n");
        fprintf(stderr, "Usage: %s [ -h | --help ]\n", argv[0]);
        fprintf(stderr, "       %s call [ address ]\n", argv[0]);
        fprintf(stderr, "       %s read [ address ]\n", argv[0]);
        fprintf(stderr, "       %s write [ address ]\n", argv[0]);
        fprintf(stderr, "\n");
        return EXIT_SUCCESS;
    }
    if (argc > 2 && argv[2][0] != '\0') {
        char          *end = NULL;
        unsigned long  val;

        errno = 0;
        val = strtoul(argv[2], &end, 0);
        if (errno) {
            fprintf(stderr, "%s: %s.\n", argv[2], strerror(errno));
            return EXIT_FAILURE;
        }
        if (end)
            while (*end == '\t' || *end == '\n' || *end == '\v' ||
                   *end == '\f' || *end == '\r' || *end == ' ')
                end++;
        if (!end || end <= argv[2] || *end) {
            fprintf(stderr, "%s: Not a valid address.\n", argv[2]);
            return EXIT_FAILURE;
        }

        jump = (void *)val;
        addr = (void *)val;
    }

    if (install_crash_handler())
        return EXIT_FAILURE;

    if (argv[1][0] == 'c' || argv[1][0] == 'C') {
        printf("Calling address %p: ", (void *)jump);
        fflush(stdout);
        jump();
        printf("Done.\n");

    } else
    if (argv[1][0] == 'r' || argv[1][0] == 'R') {
        unsigned char  val;

        printf("Reading from address %p: ", (void *)addr);
        fflush(stdout);
        val = *addr;
        printf("0x%02x, done.\n", val);

    } else
    if (argv[1][0] == 'w' || argv[1][1] == 'W') {
        printf("Writing 0xC4 to address %p: ", (void *)addr);
        fflush(stdout);
        *addr = 0xC4;
        printf("Done.\n");
    }

    printf("No crash.\n");
    return EXIT_SUCCESS;
}
gcc -Wall -O2 crasher.c -o crasher
./crasher call 0x100
Calling address 0x100: SIGSEGV: Bad jump to 0x100 probably by the instruction just before 0x400c4e.
Killed

./crasher write 0x24
Writing 0xC4 to address 0x24: SIGSEGV: Invalid write attempt to 0x24 by instruction at 0x400bad.
Killed

./crasher read 0x16
Reading from address 0x16: SIGSEGV: Invalid read attempt from 0x16 by instruction at 0x400ca3.
Killed

./crasher write 0x400ca3
Writing 0xC4 to address 0x400ca3: SIGSEGV: Invalid write attempt to 0x400ca3 by instruction at 0x400bad.
Killed

./crasher read 0x400ca3
Reading from address 0x400ca3: 0x41, done.
No crash.
What is the overhead involved in a mode switch

What is the overhead involved in a mode switch


By : BeingGeek
Date : March 29 2020, 07:55 AM
wish helps you There should be no CPU cache or TLB flush on a simple mode switch.
A quick test tells me that, on my Linux laptop it takes about 0.11 microsecond for a userspace process to complete a simple syscall that does an insignificant amount of work other than the switch to kernel mode and back. I'm using getuid(), which only copies a single integer from an in-memory struct. strace confirms that the syscall is repeated MAX times.
How much overhead is involved in creating a C# method?

How much overhead is involved in creating a C# method?


By : Steve
Date : March 29 2020, 07:55 AM
Does that help In c# they're called methods, not functions.
But yes, if you don't want to create a new class, but just call a method directly from your Main(), then you would create a static method in the same class as Main, and call it therefrom.
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