Filesystem stuff on Windows

Minor image acquire/present refactor
Unsigned integer limits
Fixed typo in arena push/push copy macro

code/os/core.h

@@ -1,6 +1,11 @@
 #if !defined(LD_OS_CORE_H_)
 #define LD_OS_CORE_H_
 
+typedef struct OS_Handle OS_Handle;
+struct OS_Handle {
+	U64 v[1];
+};
+
 // Virtual memory
 
 function U64 VM_PageSize();
@@ -11,4 +16,6 @@ function B32   VM_Commit(void *base, U64 size);
 function void  VM_Decommit(void *base, U64 size);
 function void  VM_Release(void *base, U64 size);
 
+#include "filesystem.h"
+
 #endif  // LD_OS_CORE_H_

code/os/filesystem.h

@@ -0,0 +1,16 @@
+#if !defined(LD_OS_FILESYSTEM_H_)
+#define LD_OS_FILESYSTEM_H_
+
+typedef U32 FS_AccessFlags;
+enum {
+	FS_ACCESS_READ  = (1 << 0),
+	FS_ACCESS_WRITE = (1 << 1)
+};
+
+function OS_Handle FS_FileOpen(Str8 path, FS_AccessFlags access);
+function void      FS_FileClose(OS_Handle file);
+
+function void FS_FileRead(OS_Handle file, void *ptr, U64 size, U64 offset);
+function void FS_FileWrite(OS_Handle file, void *ptr, U64 size, U64 offset);
+
+#endif  // LD_OS_FILESYSTEM_H_

code/os/impl/windows/core.c

@@ -1,3 +1,19 @@
+// Windows utilities
+
+internal Str8 Win32_WideStr(M_Arena *arena, Str8 v) {
+	Str8 result = { 0 };
+
+	S32 nchars = MultiByteToWideChar(CP_UTF8, 0, (LPCCH) v.data, (int) v.count, 0, 0) + 1;
+	U64 nbytes = nchars << 1;
+
+	result.count = nbytes - 2; // -2 because we don't include the null-terminator in the count
+	result.data  = M_ArenaPush(arena, U8, .count = nbytes);
+
+	MultiByteToWideChar(CP_UTF8, 0, (LPCCH) v.data, (int) v.count, (LPWSTR) result.data, nchars);
+
+	return result;
+}
+
 // Virtual memory
 
 U64 VM_PageSize() {
@@ -36,3 +52,4 @@ void VM_Release(void *base, U64 size) {
 	VirtualFree(base, 0, MEM_RELEASE);
 }
 
+#include "filesystem.c"

code/os/impl/windows/filesystem.c

@@ -0,0 +1,86 @@
+OS_Handle FS_FileOpen(Str8 path, FS_AccessFlags access) {
+	OS_Handle result = { 0 };
+
+	M_TempScope(0, 0) {
+		Str8 wpath = Win32_WideStr(temp.arena, path);
+
+		DWORD dwAccess = 0;
+		DWORD dwShare  = FILE_SHARE_READ;
+		DWORD dwCreate = OPEN_EXISTING;
+
+		if (access & FS_ACCESS_WRITE) {
+			dwCreate = CREATE_ALWAYS;
+			dwAccess = GENERIC_WRITE;
+		}
+
+		if (access & FS_ACCESS_READ) {
+			dwAccess |= GENERIC_READ;
+		}
+
+		HANDLE hFile = CreateFileW((LPCWSTR) wpath.data, dwAccess, dwShare, 0, dwCreate, 0, 0);
+
+		result.v[0] = (hFile == INVALID_HANDLE_VALUE) ? 0 : ((U64) hFile);
+	}
+	return result;
+}
+
+void FS_FileClose(OS_Handle file) {
+	HANDLE hFile = cast(HANDLE) file.v[0];
+	if (hFile) {
+		CloseHandle(hFile);
+	}
+}
+
+void FS_FileRead(OS_Handle file, void *ptr, U64 size, U64 offset) {
+	HANDLE hFile = cast(HANDLE) file.v[0];
+	if (hFile) {
+		U8 *buffer    = ptr;
+		U64 current   = offset;
+		U64 remainder = size;
+
+		while (remainder != 0) {
+			OVERLAPPED overlapped = { 0 };
+			overlapped.Offset     = cast(DWORD) (current & 0xFFFFFFFF);
+			overlapped.OffsetHigh = cast(DWORD) ((current >> 32) & 0xFFFFFFFF);
+
+			DWORD toread = (remainder > U32_MAX) ? U32_MAX : (DWORD) remainder;
+			DWORD nread  = 0;
+
+			if (!ReadFile(hFile, buffer, toread, &nread, &overlapped)) {
+				break;
+			}
+
+			buffer    += nread;
+			current   += nread;
+			remainder -= nread;
+		}
+	}
+}
+
+void FS_FileWrite(OS_Handle file, void *ptr, U64 size, U64 offset) {
+	HANDLE hFile = cast(HANDLE) file.v[0];
+	if (hFile) {
+		U8 *buffer    = ptr;
+		U64 current   = offset;
+		U64 remainder = size;
+
+		while (remainder != 0) {
+			OVERLAPPED overlapped = { 0 };
+			overlapped.Offset     = cast(DWORD) (current & 0xFFFFFFFF);
+			overlapped.OffsetHigh = cast(DWORD) ((current >> 32) & 0xFFFFFFFF);
+
+			DWORD towrite  = (remainder > U32_MAX) ? U32_MAX : (DWORD) remainder;
+			DWORD nwritten = 0;
+
+			if (!WriteFile(hFile, buffer, towrite, &nwritten, &overlapped)) {
+				break;
+			}
+
+			buffer    += nwritten;
+			current   += nwritten;
+			remainder -= nwritten;
+		}
+	}
+}
+
+