mul

Signed multiply

This instruction is defined by:

Encoding

svg

Synopsis

MUL performs an XLEN-bitxXLEN-bit multiplication of xs1 by xs2 and places the lower XLEN bits in the destination register. Any overflow is thrown away.

If both the high and low bits of the same product are required, then the recommended code sequence is: MULH[[S]U] xdh, xs1, xs2; MUL xdl, xs1, xs2 (source register specifiers must be in same order and xdh cannot be the same as xs1 or xs2). Microarchitectures can then fuse these into a single multiply operation instead of performing two separate multiplies.

Access

M HS U VS VU

Always

Always

Always

Always

Always

Decode Variables

Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];

Execution

  • Pruned, XLEN == 64

  • Original

XReg src1 = X[xs1];
XReg src2 = X[xs2];
X[xd] = (src1 * src2)[7'63:0];
XReg src1 = X[xs1];
XReg src2 = X[xs2];
X[xd] = (src1 * src2)[MXLEN - 1:0];