gfiber / kernel / prism / cc2c201067c613070ad79f4754c24ce9a490f48a / . / arch / blackfin / lib / 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 |