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+/*
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+ * MS-DOS support routines for PhysicsFS.
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+ *
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+ * Please see the file LICENSE.txt in the source's root directory.
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+ *
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+ * This file written by Ryan C. Gordon.
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+ */
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+
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+#define __PHYSICSFS_INTERNAL__
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+#include "physfs_platforms.h"
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+
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+#ifdef PHYSFS_PLATFORM_DOS
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+
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+#include <dirent.h>
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+#include <sys/types.h>
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+#include <sys/farptr.h>
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+#include <dpmi.h>
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+#include <go32.h>
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+
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+#include "physfs_internal.h"
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+
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+int __PHYSFS_platformInit(const char *argv0)
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+{
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+ return 1; /* always succeed. */
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+} /* __PHYSFS_platformInit */
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+
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+
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+void __PHYSFS_platformDeinit(void)
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+{
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+ /* no-op */
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+} /* __PHYSFS_platformDeinit */
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+
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+
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+void __PHYSFS_platformDetectAvailableCDs(PHYSFS_StringCallback cb, void *data)
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+{
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+#if (defined PHYSFS_NO_CDROM_SUPPORT)
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+ /* no-op. */
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+#else
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+ /* MSCDEX API calls go through interrupt 0x2F with AH=0x15: https://www.phatcode.net/res/220/files/mscdex21.txt */
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+ __dpmi_regs regs;
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+ regs.x.ax = 0x1500; /* get number of CD drive letters */
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+ regs.x.bx = 0x0000;
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+ __dpmi_int(0x2F, ®s);
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+
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+ const int num_drives = (int) regs.x.bx; /* if zero, no drives or no MSCDEX installed. */
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+ if (num_drives > 0) {
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+ regs.x.ax = 0x150D; /* get CD drive letters */
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+ regs.x.es = __tb >> 4; /* the transfer buffer is at least 2k large, if all possible drives were CD-ROMs, we'd need 26 bytes. */
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+ regs.x.bx = __tb & 0x0f;
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+ __dpmi_int(0x2F, ®s);
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+ char drives[26];
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+ dosmemget(__tb, num_drives, drives);
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+ for (int i = 0; i < num_drives; i++) {
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+ const char path[] = { 'A' + drives[i], ':', '\\', '\0' };
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+ DIR *dirp = opendir(path); /* if we can open the drive's root dir, there's a filesystem there. */
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+ if (dirp) {
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+ closedir(dirp);
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+ cb(data, path);
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+ }
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+ }
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+ }
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+#endif
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+} /* __PHYSFS_platformDetectAvailableCDs */
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+
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+
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+char *__PHYSFS_platformCalcBaseDir(const char *argv0)
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+{
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+ /* As of MS-DOS 3.0, you can get the full path to the EXE from the very end of the
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+ environment table, which is discovered through the PSP:
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+ https://en.wikipedia.org/wiki/Program_Segment_Prefix
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+
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+ An EXE is launched with the PSP's segment in DS, but we'll use a DOS API to obtain it
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+ later, since we don't control startup. https://stanislavs.org/helppc/int_21-62.html
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+
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+ The table pointed to by the word at offset 0x2C in the PSP is just a collection
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+ of ASCIZ strings, with a blank string signifying the end. The EXE path is
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+ after that.
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+
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+ https://stackoverflow.com/questions/60928997/how-to-get-environment-variables-in-a-dos-assembly-program
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+ */
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+ __dpmi_regs regs;
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+ regs.x.ax = 0x6200; /* get number of CD drive letters */
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+ regs.x.bx = 0x0000;
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+ __dpmi_int(0x21, ®s);
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+
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+ /* https://www.delorie.com/djgpp/doc/ug/dpmi/farptr-intro.html.en */
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+ const unsigned long pspseg = (unsigned long) regs.x.bx;
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+ const unsigned long envsel = (unsigned long) _farpeekw(_dos_ds, (pspseg * 16) + 0x2C);
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+
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+ int zero_count = 0;
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+ int offset;
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+ for (offset = 0; (offset < 0xFFFF) && (zero_count < 2); offset++) {
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+ const char ch = (char) _farpeekb(envsel, offset);
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+ if (ch == 0) {
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+ zero_count++;
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+ } else {
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+ zero_count = 0;
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+ }
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+ }
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+
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+ if (zero_count != 2) {
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+ return NULL; /* uhoh */
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+ }
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+
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+ /* there's a Uint16 here that represents number of extension strings. In practice it's always 1 and that one string is the path we need. */
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+ offset += 2;
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+
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+ int slen = 0;
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+ for (unsigned long i = offset; _farpeekb(envsel, i) != 0; i++) {
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+ slen++;
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+ }
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+
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+ slen++; /* count the null terminator. */
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+
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+ char *lastbackslash = NULL;
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+ char *retval = (char *) allocator.Malloc(slen);
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+ if (retval) {
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+ int i = 0;
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+ do {
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+ const char ch = (char) _farpeekb(envsel, offset + i);
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+ retval[i] = ch;
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+ if (ch == '\\') {
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+ lastbackslash = &retval[i];
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+ }
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+ i++;
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+ } while (i < slen);
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+ }
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+
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+ if (lastbackslash) {
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+ lastbackslash[1] = '\0'; /* chop off exe name, just leave path */
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+ }
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+
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+ return retval;
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+} /* __PHYSFS_platformCalcBaseDir */
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+
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+
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+char *__PHYSFS_platformCalcUserDir(void)
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+{
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+ return __PHYSFS_platformCalcBaseDir(NULL); /* !!! FIXME: ? */
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+}
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+
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+char *__PHYSFS_platformCalcPrefDir(const char *org, const char *app)
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+{
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+ return __PHYSFS_platformCalcBaseDir(NULL); /* !!! FIXME: ? */
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+} /* __PHYSFS_platformCalcPrefDir */
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+
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+
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+void *__PHYSFS_platformGetThreadID(void)
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+{
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+ return (void *) 0x1;
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+} /* __PHYSFS_platformGetThreadID */
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+
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+
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+void *__PHYSFS_platformCreateMutex(void)
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+{
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+ return (void *) 0x1;
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+} /* __PHYSFS_platformCreateMutex */
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+
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+
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+void __PHYSFS_platformDestroyMutex(void *mutex)
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+{
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+} /* __PHYSFS_platformDestroyMutex */
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+
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+
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+int __PHYSFS_platformGrabMutex(void *mutex)
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+{
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+ return (mutex == ((void *) 0x1));
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+} /* __PHYSFS_platformGrabMutex */
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+
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+
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+void __PHYSFS_platformReleaseMutex(void *mutex)
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+{
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+} /* __PHYSFS_platformReleaseMutex */
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+
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+#endif /* PHYSFS_PLATFORM_DOS */
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+
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+/* end of physfs_platform_dos.c ... */
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+
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Ryan C. Gordon