Logical-to-physical converter for single-sided floppy disk images

Prompted by discussion on simh@groups.io:
https://groups.io/g/simh/topic/need_some_help_with_rt_11/108655724

converters/lbn2pbn/Makefile

@@ -0,0 +1,20 @@
+# all of these can be over-ridden on the "make" command line if they don't suit your environment.
+TOOL=lbn2pbn
+CFLAGS=-O2 -Wall -Wextra -pedantic
+BIN=/usr/local/bin
+INSTALL=install
+CC=gcc
+
+$(TOOL): $(TOOL).c
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $(TOOL) $(TOOL).c $(LDLIBS)
+
+.PHONY: clean install uninstall
+
+clean:
+	rm -f $(TOOL)
+
+install: $(TOOL)
+	$(INSTALL) -p -m u=rx,g=rx,o=rx $(TOOL) $(BIN)
+
+uninstall:
+	rm -f $(BIN)/$(TOOL)

converters/lbn2pbn/lbn2pbn.c

@@ -0,0 +1,231 @@
+/*
+ * Sector layout converter for single-sided floppy disk images
+ * (Logical to Physical, and back)
+ *
+ * Copyright (c) 2024 Tony Lawrence
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the
+ * following conditions are met:
+ *
+ * 1.  Redistributions of source code must retain the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer.
+ *
+ * 2.  Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials
+ * provided with the distribution.
+ *
+ * 3.  Neither the name of the copyright holder nor the names
+ * of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior
+ * written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+ * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+inline
+static size_t filesize(FILE* fp)
+{
+    return fseek(fp, 0, SEEK_END) != 0 ? -1L : ftell(fp);
+}
+
+
+static int tracks = 0;
+static int sectors = 0;
+static int sector_size = 0;
+
+static int interleave = 0;
+static int track_skew = 0;
+
+static int round = 0;
+
+
+static int gcd(int a, int b)
+{
+    while (a  &&  b) {
+        if (a > b)
+            a %= b;
+        else
+            b %= a;
+    }
+    return a + b;
+}
+
+
+inline
+static int lcm(int a, int b)
+{
+    return (a * b) / gcd(a, b);
+}
+
+
+static int lbn2pbn(int lbn)
+{
+    int track;
+    int sector;
+
+    track   = lbn / sectors;
+
+    /* interleave */
+    sector  = lbn % sectors;
+    sector *= interleave;
+    sector += sector / round;
+
+    /* track skew */
+    sector += track * track_skew;
+
+    /* PBN */
+    sector %= sectors;
+    track++;
+    track  %= tracks;
+
+    return track * sectors + sector;
+}
+
+
+#ifdef __GNUC__
+__attribute__((noreturn))
+#endif
+static void usage(const char* prog)
+{
+    fprintf(stderr, "%s -T tracks -S sectors -B sector_size"
+                    " -i interleave -k track_skew [-r] infile outfile\n", prog);
+
+    fprintf(stderr, "\nTypical parameters:\n"
+                    "RX01:                   -T 77 -S 26 -B 128 -i 2 -k 6\n"
+                    "RX02 (single density):  -T 77 -S 26 -B 128 -i 2 -k 6\n"
+                    "RX02 (double density):  -T 77 -S 26 -B 256 -i 2 -k 6\n"
+                    "RX50:                   -T 80 -S 10 -B 512 -i 2 -k 2\n"
+                    "\nSupported sector sizes (in bytes): 128, 256, 512\n");
+    exit(2);
+}
+
+
+#ifndef __CYGWIN__
+extern int opterr, optind;
+extern char* optarg;
+#  ifndef _MSC_VER
+#    define _stricmp  strcmp
+#  endif
+#else
+#  define   _stricmp  strcasecmp
+#endif
+
+
+int main(int argc, char* argv[])
+{
+    int reverse = 0;
+    const char* infile;
+    const char* outfile;
+    size_t max_size;
+    size_t size;
+    FILE* in;
+    FILE* out;
+    int p, q;
+
+    p = optind;
+    while ((q = getopt(argc, argv, "T:S:B:i:k:r")) != EOF) {
+        switch (q) {
+        case 'T':
+            tracks = atoi(optarg);
+            break;
+        case 'S':
+            sectors = atoi(optarg);
+            break;
+        case 'B':
+            sector_size = atoi(optarg);
+            if ((sector_size & (sector_size - 1))
+                ||  sector_size < 128  ||  sector_size > 512) {
+                sector_size = 0;
+            }
+            break;
+        case 'i':
+            interleave = atoi(optarg);
+            break;
+        case 'k':
+            track_skew = atoi(optarg);
+            break;
+        case 'r':
+            if (!reverse) {
+                reverse = 1;
+                break;
+            }
+            /*FALLTHRU*/
+        default:
+            usage(argv[0]);
+        }
+        p = optind;
+    }
+    if (argv[p]  &&  strcmp(argv[p], "--") == 0)
+        ++p;
+    if (tracks <= 0  ||  sectors <= 0  ||  interleave <= 0  ||  track_skew < 0
+        ||  interleave >= sectors  ||  sector_size <= 0  ||  p != optind
+        ||  !(infile = argv[p++])  ||  !(outfile = argv[p++])  ||  argv[p]
+        ||  _stricmp(infile, outfile) == 0) {
+        usage(argv[0]);
+    }
+
+    if (!(in = fopen(infile, "rb"))) {
+        perror(infile);
+        return 1;
+    }
+
+    size = filesize(in);
+    q = tracks * sectors;
+    max_size = q * sector_size;
+    if (size > max_size) {
+        fprintf(stderr, "%s: file size (%zd) may not exceed %zu\n", infile, size, max_size);
+        return 1;
+    }
+
+    if (!(out = fopen(outfile, "wb"))) {
+        perror(outfile);
+        return 1;
+    }
+
+    rewind(in);
+    round = lcm(sectors, interleave);
+    for (p = 0;  p < q;  ++p) {
+        char sector[512];
+        int n = lbn2pbn(p);
+#ifdef _DEBUG
+        printf("LBN %4d (%2d / %2d)   =   PBN %4d (%2d / %2d)\n",
+               p, p / sectors, p % sectors,
+               n, n / sectors, n % sectors);
+#endif
+        if ( reverse  &&  fseek(in,  n * sector_size, SEEK_SET) != 0)
+            abort();
+        if (fread (sector, sector_size, 1, in)  != 1)
+            memset(sector, 0, sector_size);
+        if (!reverse  &&  fseek(out, n * sector_size, SEEK_SET) != 0)
+            abort();
+        if (fwrite(sector, sector_size, 1, out) != 1)
+            abort();
+    }
+
+    fclose(out);
+    fclose(in);
+    return 0;
+}