MSUB

Multiply-subtract

This instruction multiplies two register values, subtracts the product from a third register value, and writes the result to the destination register.

Encoding: Integer

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
	0	0	1	1	0	1	1	0	0	0						1
sf	op54							op31			Rm					o0	Ra					Rn					Rd

32-bit (sf == 0)

MSUB <Wd>, <Wn>, <Wm>, <Wa>

64-bit (sf == 1)

MSUB <Xd>, <Xn>, <Xm>, <Xa>

Decoding algorithm

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer a = UInt(Ra);
constant integer datasize = 32 << UInt(sf);

Operation

constant bits(datasize) operand1 = X[n, datasize];
constant bits(datasize) operand2 = X[m, datasize];
constant bits(datasize) operand3 = X[a, datasize];

constant integer result = UInt(operand3) - (UInt(operand1) * UInt(operand2));

X[d, datasize] = result;

Explanations

<Wd>: Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Wn>: Is the 32-bit name of the first general-purpose source register holding the multiplicand, encoded in the "Rn" field.
<Wm>: Is the 32-bit name of the second general-purpose source register holding the multiplier, encoded in the "Rm" field.
<Wa>: Is the 32-bit name of the third general-purpose source register holding the minuend, encoded in the "Ra" field.
<Xd>: Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.
<Xn>: Is the 64-bit name of the first general-purpose source register holding the multiplicand, encoded in the "Rn" field.
<Xm>: Is the 64-bit name of the second general-purpose source register holding the multiplier, encoded in the "Rm" field.
<Xa>: Is the 64-bit name of the third general-purpose source register holding the minuend, encoded in the "Ra" field.

Operational Notes

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.