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39 lines
2.1 KiB
ArmAsm
39 lines
2.1 KiB
ArmAsm
// Dot product summation, i.e. vOut[0] = vIn[0] + vIn[1] + vIn[2],
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// vOut[4] = vIn[4] + vIn[5] + vIn[6]. Standard implementation:
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vmudh $v29, vOne, vIn[0h]
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vmadh $v29, vOne, vIn[1h]
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vmadh vOut, vOne, vIn[2h]
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// This code pattern is a faster way, because the first instruction here does
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// not depend on vIn, so the RSP has one less stall cycle at the beginning. This
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// takes advantage of vadd writing the accumulator, which is normally useless
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// because it only writes low and leaves mid and high, so it has to be cleared
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// in advance. The built-in saturation (clamping) in vmadn does not affect this
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// result.
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// Unfortunately, even if the data being summed theoretically should not
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// overflow, imprecision in the inputs / dot product can cause overflow here,
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// which wraps, causing wrong results. So this is not useful unless you can
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// be sure the sum will never overflow. The standard implementation clamps
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// instead.
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vmudh $v29, $v31, $v31[2] // 0; clear whole accumulator
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vadd $v29, vIn, vIn[1h] // accum lo 0 = 0 + 1, 4 = 4 + 5
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vmadn vOut, vOne, vIn[2h] // + 2,6; built-in saturation (clamping) ends up not a problem
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// lpv patterns. Same works for luv. Assuming $11 is 8 byte aligned (does not have
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// to be 16 byte aligned).
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// Elem 0 1 2 3 4 5 6 7
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lpv $v27[1], (-8)($11) // 07 F8 F9 FA FB FC FD FE Byte
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lpv $v27[2], (-8)($11) // 06 07 F8 F9 FA FB FC FD addr
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lpv $v27[3], (-8)($11) // 05 06 07 F8 F9 FA FB FC relative
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lpv $v27[4], (-8)($11) // 04 05 06 07 F8 F9 FA FB to
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lpv $v27[5], (-8)($11) // 03 04 05 06 07 F8 F9 FA $11
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lpv $v27[6], (-8)($11) // 02 03 04 05 06 07 F8 F9
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lpv $v27[7], (-8)($11) // 01 02 03 04 05 06 07 F8
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lpv $v27[0], ( 0)($11) // 00 01 02 03 04 05 06 07
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lpv $v27[1], ( 0)($11) // 0F 00 01 02 03 04 05 06
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lpv $v27[2], ( 0)($11) // 0E 0F 00 01 02 03 04 05
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lpv $v27[3], ( 0)($11) // 0D 0E 0F 00 01 02 03 04
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lpv $v27[4], ( 0)($11) // 0C 0D 0E 0F 00 01 02 03
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lpv $v27[5], ( 0)($11) // 0B 0C 0D 0E 0F 00 01 02
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lpv $v27[6], ( 0)($11) // 0A 0B 0C 0D 0E 0F 00 01
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lpv $v27[7], ( 0)($11) // 09 0A 0B 0C 0D 0E 0F 00
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