muldi3.S

/*
 * Copyright 2008 Analog Devices Inc.
 *
 * Licensed under the ADI BSD license or the GPL-2 (or later)
 */

.align 2
.global ___muldi3;
.type ___muldi3, STT_FUNC;

#ifdef CONFIG_ARITHMETIC_OPS_L1
.section .l1.text
#else
.text
#endif

/*
	   R1:R0 * R3:R2
	 = R1.h:R1.l:R0.h:R0.l * R3.h:R3.l:R2.h:R2.l
[X]	 = (R1.h * R3.h) * 2^96
[X]	   + (R1.h * R3.l + R1.l * R3.h) * 2^80
[X]	   + (R1.h * R2.h + R1.l * R3.l + R3.h * R0.h) * 2^64
[T1]	   + (R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h) * 2^48
[T2]	   + (R1.l * R2.l + R3.l * R0.l + R0.h * R2.h) * 2^32
[T3]	   + (R0.l * R2.h + R2.l * R0.h) * 2^16
[T4]	   + (R0.l * R2.l)

	We can discard the first three lines marked "X" since we produce
	only a 64 bit result.  So, we need ten 16-bit multiplies.

	Individual mul-acc results:
[E1]	 =  R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h
[E2]	 =  R1.l * R2.l + R3.l * R0.l + R0.h * R2.h
[E3]	 =  R0.l * R2.h + R2.l * R0.h
[E4]	 =  R0.l * R2.l

	We also need to add high parts from lower-level results to higher ones:
	E[n]c = E[n] + (E[n+1]c >> 16), where E4c := E4

	One interesting property is that all parts of the result that depend
	on the sign of the multiplication are discarded.  Those would be the
	multiplications involving R1.h and R3.h, but only the top 16 bit of
	the 32 bit result depend on the sign, and since R1.h and R3.h only
	occur in E1, the top half of these results is cut off.
	So, we can just use FU mode for all of the 16-bit multiplies, and
	ignore questions of when to use mixed mode.  */

___muldi3:
	/* [SP] technically is part of the caller's frame, but we can
	   use it as scratch space.  */
	A0 = R2.H * R1.L, A1 = R2.L * R1.H (FU) || R3 = [SP + 12];	/* E1 */
	A0 += R3.H * R0.L, A1 += R3.L * R0.H (FU) || [SP] = R4;		/* E1 */
	A0 += A1;							/* E1 */
	R4 = A0.w;
	A0 = R0.l * R3.l (FU);						/* E2 */
	A0 += R2.l * R1.l (FU);						/* E2 */

	A1 = R2.L * R0.L (FU);						/* E4 */
	R3 = A1.w;
	A1 = A1 >> 16;							/* E3c */
	A0 += R2.H * R0.H, A1 += R2.L * R0.H (FU);			/* E2, E3c */
	A1 += R0.L * R2.H (FU);						/* E3c */
	R0 = A1.w;
	A1 = A1 >> 16;							/* E2c */
	A0 += A1;							/* E2c */
	R1 = A0.w;

	/* low(result) = low(E3c):low(E4) */
	R0 = PACK (R0.l, R3.l);
	/* high(result) = E2c + (E1 << 16) */
	R1.h = R1.h + R4.l (NS) || R4 = [SP];
	RTS;

.size ___muldi3, .-___muldi3