Some byte shaving; lseek returns the offset.

plat/cpm/libsys/lseek.c

@@ -24,5 +24,5 @@ off_t lseek(int fd, off_t offset, int whence)
     
     U16(fcbe->fcb.r) = offset>>7;
     fcbe->offset = offset & 0x7f;
-    return 0;
+    return offset;
 }

plat/cpm/libsys/read.c

@@ -17,6 +17,7 @@ ssize_t read(int fd, void* buffer, size_t count)
 	struct FCBE* fcbe = &__fd[fd];
 	uint8_t olduser;
 	ssize_t result;
+	uint8_t* src;
 
     __init_file_descriptors();
 	if (fcbe->fcb.dr == 0)
@@ -36,8 +37,6 @@ ssize_t read(int fd, void* buffer, size_t count)
 		goto done;
 	if (fcbe->offset || !SECTOR_ALIGNED(count))
 	{
-		uint8_t delta;
-
 		/* We need to read bytes until we're at a sector boundary. */
 
 		cpm_set_dma(__transfer_buffer);
@@ -46,13 +45,13 @@ ssize_t read(int fd, void* buffer, size_t count)
 
 		/* Copy enough bytes to reach the end of the sector. */
 
-		delta = 128 - fcbe->offset;
+		src = __transfer_buffer + fcbe->offset;
-		if (delta > count)
+		while ((count != 0) && (fcbe->offset != 128))
-			delta = count;
+		{
-		memcpy(bbuffer, __transfer_buffer+fcbe->offset, delta);
+			*bbuffer++ = *src++;
-		fcbe->offset += delta;
+			fcbe->offset++;
-		count -= delta;
+			count--;
-		bbuffer += delta;
+		}
 
 		/* If we've read enough bytes, advance to the next sector. */
 
@@ -89,7 +88,13 @@ ssize_t read(int fd, void* buffer, size_t count)
 		if (cpm_read_random_safe(&fcbe->fcb) != 0)
 			goto eio;
 
-		memcpy(bbuffer, __transfer_buffer, count);
+		src = __transfer_buffer;
+		while (count != 0)
+		{
+			*bbuffer++ = *src++;
+			count--;
+		}
+
 		fcbe->offset = count;
 	}
 

plat/cpm/libsys/write.c

@@ -19,10 +19,11 @@ void _sys_write_tty(char c)
 
 ssize_t write(int fd, void* buffer, size_t count)
 {
-	uint8_t* bbuffer = buffer;
+	const uint8_t* bbuffer = buffer;
 	struct FCBE* fcbe = &__fd[fd];
 	uint8_t olduser;
 	uint16_t result;
+	uint8_t* dest;
 
     __init_file_descriptors();
 	if (fcbe->fcb.dr == 0)
@@ -40,8 +41,6 @@ ssize_t write(int fd, void* buffer, size_t count)
 
 	if (fcbe->offset || !SECTOR_ALIGNED(count))
 	{
-		uint8_t delta;
-
 		/* We're not at a sector boundary, so we need to do a
 		 * read/modify/write of the initial fragment. */
 
@@ -51,13 +50,13 @@ ssize_t write(int fd, void* buffer, size_t count)
 
 		/* Copy enough bytes to reach the end of the sector. */
 
-		delta = 128 - fcbe->offset;
+		dest = __transfer_buffer + fcbe->offset;
-		if (delta > count)
+		while ((count != 0) && (fcbe->offset != 128))
-			delta = count;
+		{
-		memcpy(__transfer_buffer+fcbe->offset, bbuffer, delta);
+			*dest++ = *bbuffer++;
-		fcbe->offset += delta;
+			fcbe->offset++;
-		count -= delta;
+			count--;
-		bbuffer += delta;
+		}
 
 		/* Write back. */
 
@@ -94,7 +93,12 @@ ssize_t write(int fd, void* buffer, size_t count)
 		if (cpm_read_random_safe(&fcbe->fcb) != 0)
 			goto eio;
 
-		memcpy(__transfer_buffer, bbuffer, count);
+		dest = __transfer_buffer;
+		while (count != 0)
+		{
+			*dest++ = *bbuffer++;
+			count--;
+		}
 
 		if (cpm_write_random(&fcbe->fcb) != 0)
 			goto eio;