|
P32A 001000 |
rt |
rs |
ac |
10 |
011 |
010 |
111 |
111 |
|
6 |
5 |
5 |
2 |
2 |
3 |
3 |
3 |
3 |
DPSQX_S.W.PH ac, rs, rt |
DSP-R2 |
Cross Dot Product with Subtraction on Fractional Halfword Elements |
Cross Dot Product with Subtraction on Fractional Halfword Elements
Element-wise cross multiplication of two vectors of fractional halfword elements and subtraction of the accumulated
32-bit intermediate products from the specified 64-bit accumulator register, with saturation.
ac = ac - (sat32(rs31..16 * rt15..0) + sat32(rs15..0 * rt31..16))
The left Q15 fractional word value from registers rt is multiplied with the right halfword element from register rs and the result left-shifted by one bit position to generate a Q31 fractional format intermediate product. Similarly, the right
Q15 fractional word value from registers rt is multiplied with the left halfword element from register rs and the result left-shifted by one bit position to generate a Q31 fractional format intermediate product. If both multiplicands for either of the multiplications are equal to -1.0 (0x8000 hexadecimal), the resulting intermediate product is saturated to the maximum positive Q31 fractional value (0x7FFFFFFF hexadecimal).
The two intermediate products are then sign-extended and summed to generate a 64-bit, Q32.31 fractional format dotproduct result that is subtracted from the specified 64-bit HI/LO accumulator to produce a f inal Q32.31 fractional result.
The value of ac can range from 0 to 3; a v alue of 0 refers to the original HI/LO register pair of the MIPS32 architecture.
If saturation occurs as a result of a half word multiplication, a 1 is wr itten to one o f bits 16 through 19 of the
DSPControl register, within the ouflag field. The value of ac determines which of these bits is set: bit 16 corresponds
to ac0, bit 17 to ac1, bit 18 to ac2, and bit 19 to ac3.
No data-dependent exceptions are possible.
The operands must be values in the specified format. If they are not, the result is UNPREDICTABLE and the values of the operand vectors become UNPREDICTABLE.
ValidateAccessToDSPResources()
tempB31..0 = multiplyQ15Q15( ac, GPR[rs]31..16, GPR[rt]15..0 )
tempA31..0 = multiplyQ15Q15( ac, GPR[rs]15..0, GPR[rt]31..16 )
dotp63..0 = ( (tempB31)32 || tempB31..0 ) + ( (tempA31)32 || tempA31..0 )
tempC63..0 = ( HI[ac]31..0 || LO[ac]31..0 ) - dotp63..0
( HI[ac]31..0 || LO[ac]31..0 ) = tempC63..32 || tempC31..0
function multiplyQ15Q15( acc1..0, a15..0, b15..0 )
if ( a15..0 = 0x8000 ) and ( b15..0 = 0x8000 ) then
temp31..0 = 0x7FFFFFFF
DSPControlouflag:16+acc = 1
else
temp31..0 = ( a15..0 * b15..0 ) << 1
endif
return temp31..0
endfunction multiplyQ15Q15