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author | Bernd Schmidt <bernds_cb1@t-online.de> | 2009-01-07 23:14:39 +0800 |
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committer | Bryan Wu <cooloney@kernel.org> | 2009-01-07 23:14:39 +0800 |
commit | 71ae92f51a5f2d824972cf60b25cc40def62ba29 (patch) | |
tree | 8c9434ecb5035c2868a5ff4ddd18236d16f52dd4 /arch/blackfin/lib/muldi3.S | |
parent | 36478585d994f82654cf8435b34c1a8df3c6ae69 (diff) | |
download | linux-3.10-71ae92f51a5f2d824972cf60b25cc40def62ba29.tar.gz linux-3.10-71ae92f51a5f2d824972cf60b25cc40def62ba29.tar.bz2 linux-3.10-71ae92f51a5f2d824972cf60b25cc40def62ba29.zip |
Blackfin arch: Replace C version of 64 bit multiply with hand optimized assembly
Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Diffstat (limited to 'arch/blackfin/lib/muldi3.S')
-rw-r--r-- | arch/blackfin/lib/muldi3.S | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/arch/blackfin/lib/muldi3.S b/arch/blackfin/lib/muldi3.S new file mode 100644 index 00000000000..abde120ee23 --- /dev/null +++ b/arch/blackfin/lib/muldi3.S @@ -0,0 +1,68 @@ +.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 |