Encoding:

Format:

MSUB_Q.df 

MSUB_Q.H wd,ws,wt

MSUB_Q.W wd,ws,wt

Purpose:

Vector Fixed-Point Multiply and Subtract

Vector fixed-point multiply and subtract.

Description:

wd[i] = saturate(wd[i] - ws[i] * wt[i])

The product of fixed-point elements in vector wt by fixed-point elements in vector ws are subtracted from the fixedpoint elements in vector wd. The multiplication result is not saturated, i.e. exact (-1) * (-1) = 1 is subtracted from the destination. The saturated fixed-point results are stored back to wd.

Internally, the multiplication and subtraction operate on data double the size of df. Truncation to fixed-point data format df is performed at the very last stage, after saturation.

The operands and results are values in fixed-point data format df.

Restrictions:

No data-dependent exceptions are possible.

Operation:

MSUB_Q.H
   for i in 0 .. WRLEN/16-1
      WR[wd]16i+15..16i = 
             q_msub(WR[wd]16i+15..16i, WR[ws]16i+15..16i, WR[wt]16i+15..16i, 16)
   endfor
MSUB_Q.W
   for i in 0 .. WRLEN/32-1
      WR[wd]32i+31..32i = 
             q_msub(WR[wd]32i+31..32i, WR[ws]32i+31..32i, WR[wt]32i+31..32i, 32)
   endfor
function mulx_s(ts, tt, n)
   s = (tsn-1)n || tsn-1..0 
   t = (ttn-1)n || ttn-1..0
   p = s * t 
   return p2n-1..0
endfunction mulx_s
function sat_s(tt, n, b)
   if ttn-1 = 0 and ttn-1..b-1 != 0n-b+1 then
      return 0n-b+1 || 1b-1
   endif
   if ttn-1 = 1 and ttn-1..b-1 != 1n-b+1 then
      return 1n-b+1 || 0b-1
   else
      return tt
   endif
endfunction sat_s
function q_msub(td, ts, tt, n)
   p = mulx_s(ts, tt, n)
   d = (tdn-1 || tdn-1..0 || 0n-1) - p2n-1..0
   d = sat_s(d2n-1..n-1, n+1, n)
   return dn-1..0
endfunction q_msub

Exceptions:

Reserved Instruction Exception, MSA Disabled Exception.