69 строки
2.2 KiB
ArmAsm
69 строки
2.2 KiB
ArmAsm
.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
|