=== expression w/ multiply and divide operations ===

#define	TXTBASE		((unsigned int *)0x0400)
#define	TXTWIDTH	32
#define	TXTLINES	16
#define	TXTSIZE		((unsigned int)TXTWIDTH*TXTLINES)
#define	TXTEND		(TXTBASE+TXTSIZE)

static unsigned char *_getpos(unsigned char x, unsigned char y)
{
	unsigned char *pos;

	pos = TXTBASE + ((y / 2) * TXTWIDTH) + (x / 2);

	if (pos > TXTEND)
		return NULL;

	return pos;
}

--- non-optimized ---

?0_getpos LEAS -2,S
 LDB 5,S
 CLRA
 TFR D,X
 LDB #2
 CLRA
 JSR ?div
 TFR D,X
 LDB #32
 CLRA
 JSR ?mul
 ADDD #1024
 PSHS A,B
 LDB 9,S
 CLRA
 TFR D,X
 LDB #2
 CLRA
 JSR ?div
 ADDD ,S++
 STD 0,S
 LDD 0,S
 TFR D,X
 LDD #1536
 JSR ?ugt
 LBEQ ?8
 LDD #0
 JMP ?9
?8 EQU *
 LDD 0,S
?9 EQU *
 LEAS 2,S
 RTS

--- optimized ---

?0_getpos LEAS -2,S
 LDB 5,S
 CLRA
 TFR D,X
 LDD #(2)&255
 JSR ?div
 TFR D,X
 LDD #(32)&255
 JSR ?mul
 ADDD #1024
 PSHS A,B
 LDB 9,S
 CLRA
 TFR D,X
 LDD #(2)&255
 JSR ?div
 ADDD ,S++
 STD ,S
 CMPD #1536
 LBLS ?8
 CLRA
 CLRB
 JMP ?9
?8 EQU *
 LDD ,S
?9 EQU *
 PULS X,PC

=== expression w/ logical operations ===

#define	TXTBASE		((unsigned int *)0x0400)
#define	TXTWIDTH	32
#define	TXTLINES	16
#define	TXTSIZE		((unsigned int)TXTWIDTH*TXTLINES)
#define	TXTEND		(TXTBASE+TXTSIZE)

static unsigned char *_getpos(unsigned char x, unsigned char y)
{
	unsigned char *pos;

	/*
	 * Hand-optimized expression, equivalent to this:
	 *
	 * pos = TXTBASE + ((y / 2) * TXTWIDTH) + (x / 2);
	 *
	 */
	pos = TXTBASE + ((y & 0xfe) << 4) + (x >> 1);

	if (pos > TXTEND)
		return NULL;

	return pos;
}

--- non-optimized ---

?0_getpos LEAS -2,S
 LDB 5,S
 ANDB #254
 CLRA
 TFR D,X
 LDB #4
 CLRA
 JSR ?shl
 ADDD #1024
 PSHS A,B
 LDB 9,S
 CLRA
 TFR D,X
 LDB #1
 CLRA
 JSR ?shr
 ADDD ,S++
 STD 0,S
 LDD 0,S
 TFR D,X
 LDD #1536
 JSR ?ugt
 LBEQ ?8
 LDD #0
 JMP ?9
?8 EQU *
 LDD 0,S
?9 EQU *
 LEAS 2,S
 RTS

--- optimized ---

?0_getpos LEAS -2,S
 LDB 5,S
 ANDB #254
 CLRA
 TFR D,X
 LDD #(4)&255
 JSR ?shl
 ADDD #1024
 PSHS A,B
 LDB 9,S
 CLRA
 TFR D,X
 LDD #(1)&255
 JSR ?shr
 ADDD ,S++
 STD ,S
 CMPD #1536
 LBLS ?8
 CLRA
 CLRB
 JMP ?9
?8 EQU *
 LDD ,S
?9 EQU *
 PULS X,PC