UMAXV

Unsigned maximum across vector

This instruction compares all the vector elements in the source SIMD&FP register, and writes the largest of the values as a scalar to the destination SIMD&FP register. All the values in this instruction are unsigned integer values.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

Encoding: Advanced SIMD

Variants: FEAT_AdvSIMD (ARMv8.0)

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		1	0	1	1	1	0			1	1	0	0	0	0	1	0	1	0	1	0
	Q	U						size							op							Rn					Rd

UMAXV <V><d>, <Vn>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if size:Q == '100' then EndOfDecode(Decode_UNDEF);
if size == '11' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer esize = 8 << UInt(size);
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

constant boolean unsigned = TRUE;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand = V[n, datasize];
integer max = Int(Elem[operand, 0, esize], unsigned);

for e = 1 to elements-1
    constant integer element = Int(Elem[operand, e, esize], unsigned);
    max = Max(max, element);

V[d, esize] = max;

Explanations

<V>: <d>: Is the number of the SIMD&FP destination register, encoded in the "Rd" field.
<Vn>: Is the name of the SIMD&FP source register, encoded in the "Rn" field.
<T>:

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.