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96f1050d RG |
1 | /* |
2 | * Copyright 2008 Analog Devices Inc. | |
3 | * | |
de450838 | 4 | * Licensed under the Clear BSD license or the GPL-2 (or later) |
96f1050d RG |
5 | */ |
6 | ||
71ae92f5 BS |
7 | .align 2 |
8 | .global ___muldi3; | |
9 | .type ___muldi3, STT_FUNC; | |
10 | ||
11 | #ifdef CONFIG_ARITHMETIC_OPS_L1 | |
12 | .section .l1.text | |
13 | #else | |
14 | .text | |
15 | #endif | |
16 | ||
17 | /* | |
18 | R1:R0 * R3:R2 | |
19 | = R1.h:R1.l:R0.h:R0.l * R3.h:R3.l:R2.h:R2.l | |
20 | [X] = (R1.h * R3.h) * 2^96 | |
21 | [X] + (R1.h * R3.l + R1.l * R3.h) * 2^80 | |
22 | [X] + (R1.h * R2.h + R1.l * R3.l + R3.h * R0.h) * 2^64 | |
23 | [T1] + (R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h) * 2^48 | |
24 | [T2] + (R1.l * R2.l + R3.l * R0.l + R0.h * R2.h) * 2^32 | |
25 | [T3] + (R0.l * R2.h + R2.l * R0.h) * 2^16 | |
26 | [T4] + (R0.l * R2.l) | |
27 | ||
28 | We can discard the first three lines marked "X" since we produce | |
29 | only a 64 bit result. So, we need ten 16-bit multiplies. | |
30 | ||
31 | Individual mul-acc results: | |
32 | [E1] = R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h | |
33 | [E2] = R1.l * R2.l + R3.l * R0.l + R0.h * R2.h | |
34 | [E3] = R0.l * R2.h + R2.l * R0.h | |
35 | [E4] = R0.l * R2.l | |
36 | ||
37 | We also need to add high parts from lower-level results to higher ones: | |
38 | E[n]c = E[n] + (E[n+1]c >> 16), where E4c := E4 | |
39 | ||
40 | One interesting property is that all parts of the result that depend | |
41 | on the sign of the multiplication are discarded. Those would be the | |
42 | multiplications involving R1.h and R3.h, but only the top 16 bit of | |
43 | the 32 bit result depend on the sign, and since R1.h and R3.h only | |
44 | occur in E1, the top half of these results is cut off. | |
45 | So, we can just use FU mode for all of the 16-bit multiplies, and | |
46 | ignore questions of when to use mixed mode. */ | |
47 | ||
48 | ___muldi3: | |
49 | /* [SP] technically is part of the caller's frame, but we can | |
50 | use it as scratch space. */ | |
51 | A0 = R2.H * R1.L, A1 = R2.L * R1.H (FU) || R3 = [SP + 12]; /* E1 */ | |
52 | A0 += R3.H * R0.L, A1 += R3.L * R0.H (FU) || [SP] = R4; /* E1 */ | |
53 | A0 += A1; /* E1 */ | |
54 | R4 = A0.w; | |
55 | A0 = R0.l * R3.l (FU); /* E2 */ | |
56 | A0 += R2.l * R1.l (FU); /* E2 */ | |
57 | ||
58 | A1 = R2.L * R0.L (FU); /* E4 */ | |
59 | R3 = A1.w; | |
60 | A1 = A1 >> 16; /* E3c */ | |
61 | A0 += R2.H * R0.H, A1 += R2.L * R0.H (FU); /* E2, E3c */ | |
62 | A1 += R0.L * R2.H (FU); /* E3c */ | |
63 | R0 = A1.w; | |
64 | A1 = A1 >> 16; /* E2c */ | |
65 | A0 += A1; /* E2c */ | |
66 | R1 = A0.w; | |
67 | ||
68 | /* low(result) = low(E3c):low(E4) */ | |
69 | R0 = PACK (R0.l, R3.l); | |
70 | /* high(result) = E2c + (E1 << 16) */ | |
71 | R1.h = R1.h + R4.l (NS) || R4 = [SP]; | |
72 | RTS; | |
73 | ||
74 | .size ___muldi3, .-___muldi3 |