69 lines
2.2 KiB
ArmAsm
69 lines
2.2 KiB
ArmAsm
.align 2
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.global ___muldi3;
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.type ___muldi3, STT_FUNC;
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#ifdef CONFIG_ARITHMETIC_OPS_L1
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.section .l1.text
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#else
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.text
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#endif
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/*
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R1:R0 * R3:R2
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= R1.h:R1.l:R0.h:R0.l * R3.h:R3.l:R2.h:R2.l
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[X] = (R1.h * R3.h) * 2^96
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[X] + (R1.h * R3.l + R1.l * R3.h) * 2^80
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[X] + (R1.h * R2.h + R1.l * R3.l + R3.h * R0.h) * 2^64
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[T1] + (R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h) * 2^48
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[T2] + (R1.l * R2.l + R3.l * R0.l + R0.h * R2.h) * 2^32
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[T3] + (R0.l * R2.h + R2.l * R0.h) * 2^16
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[T4] + (R0.l * R2.l)
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We can discard the first three lines marked "X" since we produce
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only a 64 bit result. So, we need ten 16-bit multiplies.
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Individual mul-acc results:
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[E1] = R1.h * R2.l + R3.h * R0.l + R1.l * R2.h + R3.l * R0.h
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[E2] = R1.l * R2.l + R3.l * R0.l + R0.h * R2.h
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[E3] = R0.l * R2.h + R2.l * R0.h
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[E4] = R0.l * R2.l
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We also need to add high parts from lower-level results to higher ones:
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E[n]c = E[n] + (E[n+1]c >> 16), where E4c := E4
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One interesting property is that all parts of the result that depend
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on the sign of the multiplication are discarded. Those would be the
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multiplications involving R1.h and R3.h, but only the top 16 bit of
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the 32 bit result depend on the sign, and since R1.h and R3.h only
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occur in E1, the top half of these results is cut off.
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So, we can just use FU mode for all of the 16-bit multiplies, and
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ignore questions of when to use mixed mode. */
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___muldi3:
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/* [SP] technically is part of the caller's frame, but we can
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use it as scratch space. */
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A0 = R2.H * R1.L, A1 = R2.L * R1.H (FU) || R3 = [SP + 12]; /* E1 */
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A0 += R3.H * R0.L, A1 += R3.L * R0.H (FU) || [SP] = R4; /* E1 */
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A0 += A1; /* E1 */
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R4 = A0.w;
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A0 = R0.l * R3.l (FU); /* E2 */
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A0 += R2.l * R1.l (FU); /* E2 */
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A1 = R2.L * R0.L (FU); /* E4 */
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R3 = A1.w;
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A1 = A1 >> 16; /* E3c */
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A0 += R2.H * R0.H, A1 += R2.L * R0.H (FU); /* E2, E3c */
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A1 += R0.L * R2.H (FU); /* E3c */
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R0 = A1.w;
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A1 = A1 >> 16; /* E2c */
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A0 += A1; /* E2c */
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R1 = A0.w;
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/* low(result) = low(E3c):low(E4) */
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R0 = PACK (R0.l, R3.l);
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/* high(result) = E2c + (E1 << 16) */
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R1.h = R1.h + R4.l (NS) || R4 = [SP];
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RTS;
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.size ___muldi3, .-___muldi3
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