Introduce example program for viewing BBS art

examples/art.c

@@ -0,0 +1,208 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <iconv.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+#include <time.h>
+#include <unistd.h>
+
+/**
+ * @fileoverview program for viewing bbs art files
+ * @see http://www.textfiles.com/art/
+ */
+
+#define INBUFSZ 256
+#define OUBUFSZ (INBUFSZ * 6)
+#define SLIT(s) ((unsigned)s[3] << 24 | s[2] << 16 | s[1] << 8 | s[0])
+
+volatile sig_atomic_t got_signal;
+
+void on_signal(int sig) {
+  got_signal = 1;
+}
+
+void process_file(const char *path, int fd, iconv_t cd, int baud_rate) {
+  char input_buffer[INBUFSZ];
+  char output_buffer[OUBUFSZ];
+  size_t input_left, output_left;
+  char *input_ptr, *output_ptr;
+  struct timespec next = timespec_mono();
+
+  for (;;) {
+
+    // read from file
+    ssize_t bytes_read = read(fd, input_buffer, INBUFSZ);
+    if (bytes_read == -1) {
+      perror(path);
+      exit(1);
+    }
+    if (!bytes_read)
+      break;
+
+    // modernize character set
+    input_ptr = input_buffer;
+    input_left = bytes_read;
+    output_ptr = output_buffer;
+    output_left = OUBUFSZ;
+    if (iconv(cd, &input_ptr, &input_left, &output_ptr, &output_left) ==
+        (size_t)-1) {
+      perror(path);
+      exit(1);
+    }
+
+    // write to terminal
+    for (char *p = output_buffer; p < output_ptr; p++) {
+      if (got_signal)
+        return;
+
+      write(STDOUT_FILENO, p, 1);
+
+      // allow arrow keys to change baud rate
+      char key[4] = {0};
+      if (read(STDIN_FILENO, key, sizeof(key)) > 0) {
+        if (SLIT(key) == SLIT("\e[A") ||  // up
+            SLIT(key) == SLIT("\e[C")) {  // right
+          baud_rate *= 1.4;
+        } else if (SLIT(key) == SLIT("\e[B") ||  // down
+                   SLIT(key) == SLIT("\e[D")) {  // left
+          baud_rate *= 0.6;
+        }
+      }
+
+      // insert artificial delay for one byte. we divide by 10 to convert
+      // bits to bytes, because that is how many bits 8-N-1 encoding used
+      next = timespec_add(next, timespec_fromnanos(1e9 / (baud_rate / 10.)));
+      usleep(timespec_tomicros(timespec_subz(next, timespec_mono())));
+    }
+  }
+}
+
+int main(int argc, char *argv[]) {
+
+  // "When new technology comes out, people don't all buy it right away.
+  //  If what they have works, some will wait until it doesn't. A few
+  //  people do get the latest though. In 1984 2400 baud modems became
+  //  available, so some people had them, but many didn't. A BBS list
+  //  from 1986 shows operators were mostly 300 and 1200, but some were
+  //  using 2400. The next 5 years were the hayday of the 2400."
+  //
+  // https://forum.vcfed.org/index.php?threads/the-2400-baud-modem.44241/
+
+  int baud_rate = 2400;                // -b 2400
+  const char *from_charset = "CP437";  // -f CP437
+  const char *to_charset = "UTF-8";    // -t UTF-8
+
+  int opt;
+  while ((opt = getopt(argc, argv, "hb:f:t:")) != -1) {
+    switch (opt) {
+      case 'b': {
+        char *endptr;
+        double rate = strtod(optarg, &endptr);
+        if (*endptr == 'k') {
+          rate *= 1e3;
+          ++endptr;
+        } else if (*endptr == 'm') {
+          rate *= 1e6;
+          ++endptr;
+        }
+        if (*endptr || baud_rate <= 0) {
+          fprintf(stderr, "%s: invalid baud rate: %s\n", argv[0], optarg);
+          exit(1);
+        }
+        baud_rate = rate;
+        break;
+      }
+      case 'f':
+        from_charset = optarg;
+        break;
+      case 't':
+        to_charset = optarg;
+        break;
+      case 'h':
+        fprintf(stderr, "\
+Usage:\n\
+    %s [-b BAUD] [-f CP437] [-t UTF-8] FILE...\n\
+\n\
+Supported charsets:\n\
+    utf8, wchart, ucs2be, ucs2le, utf16be, utf16le, ucs4be, ucs4le,\n\
+    ascii, utf16, ucs4, ucs2, eucjp, shiftjis, iso2022jp, gb18030, gbk,\n\
+    gb2312, big5, euckr, iso88591, latin1, iso88592, iso88593, iso88594,\n\
+    iso88595, iso88596, iso88597, iso88598, iso88599, iso885910,\n\
+    iso885911, iso885913, iso885914, iso885915, iso885916, cp1250,\n\
+    windows1250, cp1251, windows1251, cp1252, windows1252, cp1253,\n\
+    windows1253, cp1254, windows1254, cp1255, windows1255, cp1256,\n\
+    windows1256, cp1257, windows1257, cp1258, windows1258, koi8r, koi8u,\n\
+    cp437, cp850, cp866, ibm1047, cp1047.\n\
+\n\
+See also:\n\
+    http://www.textfiles.com/art/\n\
+\n",
+                argv[0]);
+        exit(0);
+      default:
+        fprintf(stderr, "protip: pass the -h flag for help\n");
+        exit(1);
+    }
+  }
+  if (optind == argc) {
+    fprintf(stderr, "%s: missing operand\n", argv[0]);
+    exit(1);
+  }
+
+  iconv_t cd = iconv_open(to_charset, from_charset);
+  if (cd == (iconv_t)-1) {
+    fprintf(stderr, "error: conversion from %s to %s not supported\n",
+            from_charset, to_charset);
+    exit(1);
+  }
+
+  // catch ctrl-c
+  signal(SIGINT, on_signal);
+
+  // don't wait until newline to read() keystrokes
+  struct termios t;
+  if (!tcgetattr(STDIN_FILENO, &t)) {
+    struct termios t2 = t;
+    t2.c_lflag &= ~(ICANON | ECHO);
+    tcsetattr(STDIN_FILENO, TCSANOW, &t2);
+  }
+
+  // make stdin nonblocking
+  fcntl(STDIN_FILENO, F_SETFL, fcntl(STDIN_FILENO, F_GETFL) | O_NONBLOCK);
+
+  // hide cursor
+  write(STDOUT_FILENO, "\e[?25l", 6);
+
+  // Process each file specified on the command line
+  for (int i = optind; i < argc && !got_signal; i++) {
+    int fd = open(argv[i], O_RDONLY);
+    if (fd == -1) {
+      perror(argv[i]);
+      continue;
+    }
+    process_file(argv[i], fd, cd, baud_rate);
+    close(fd);
+  }
+
+  // cleanup
+  iconv_close(cd);
+
+  // show cursor
+  write(STDOUT_FILENO, "\e[?25h", 6);
+
+  // restore terminal
+  tcsetattr(STDIN_FILENO, TCSANOW, &t);
+}

libc/calls/usleep.c

@@ -34,10 +34,14 @@
  * @norestart
  */
 int usleep(uint64_t micros) {
+  // All OSes except OpenBSD return instantly on usleep(0). So we might
+  // as well avoid system call overhead and helping OpenBSD work better
+  if (micros) {
     errno_t err;
     struct timespec ts = timespec_frommicros(micros);
-  err = clock_nanosleep(CLOCK_REALTIME, 0, &ts, 0);
+    err = clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, 0);
     if (err)
       return errno = err, -1;
+  }
   return 0;
 }