FRECPS
Floating-point Reciprocal Step. This instruction multiplies the corresponding floating-point values in the vectors of the two source SIMD&FP registers, subtracts each of the products from 2.0, places the resulting floating-point values in a vector, and writes the vector to the destination SIMD&FP register.
This instruction can generate a floating-point exception. Depending on the settings in FPCR, the exception results in either a flag being set in FPSR, or a synchronous exception being generated. For more information, see Floating-point exception traps.
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.
It has encodings from 4 classes:
Scalar half precision
,
Scalar single-precision and double-precision
,
Vector half precision
and
Vector single-precision and double-precision
Scalar half precision
(Armv8.2)
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 | 1 | 0 | 0 | 1 | 0 | Rm | 0 | 0 | 1 | 1 | 1 | 1 | Rn | Rd |
if !HaveFP16Ext() then UNDEFINED;
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer esize = 16;
integer datasize = esize;
integer elements = 1;
Scalar single-precision and double-precision
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 | 1 | 0 | 0 | sz | 1 | Rm | 1 | 1 | 1 | 1 | 1 | 1 | Rn | Rd |
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer esize = 32 << UInt(sz);
integer datasize = esize;
integer elements = 1;
Vector half precision
(Armv8.2)
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 | Q | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | Rm | 0 | 0 | 1 | 1 | 1 | 1 | Rn | Rd |
if !HaveFP16Ext() then UNDEFINED;
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer esize = 16;
integer datasize = if Q == '1' then 128 else 64;
integer elements = datasize DIV esize;
Vector single-precision and double-precision
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 | Q | 0 | 0 | 1 | 1 | 1 | 0 | 0 | sz | 1 | Rm | 1 | 1 | 1 | 1 | 1 | 1 | Rn | Rd |
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
if sz:Q == '10' then UNDEFINED;
integer esize = 32 << UInt(sz);
integer datasize = if Q == '1' then 128 else 64;
integer elements = datasize DIV esize;
Assembler Symbols
<Hd> |
Is the 16-bit name of the SIMD&FP destination register, encoded in the "Rd" field.
|
<Hn> |
Is the 16-bit name of the first SIMD&FP source register, encoded in the "Rn" field.
|
<Hm> |
Is the 16-bit name of the second SIMD&FP source register, encoded in the "Rm" field.
|
<V> |
Is a width specifier,
encoded in
sz :
|
<d> |
Is the number of the SIMD&FP destination register, in the "Rd" field.
|
<n> |
Is the number of the first SIMD&FP source register, encoded in the "Rn" field.
|
<m> |
Is the number of the second SIMD&FP source register, encoded in the "Rm" field.
|
<Vd> |
Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
|
<T> |
For the vector half precision variant: is an arrangement specifier,
encoded in
Q :
|
|
For the vector single-precision and double-precision variant: is an arrangement specifier,
encoded in
sz:Q :
sz |
Q |
<T> |
0 |
0 |
2S |
0 |
1 |
4S |
1 |
0 |
RESERVED |
1 |
1 |
2D |
|
<Vn> |
Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
|
<Vm> |
Is the name of the second SIMD&FP source register, encoded in the "Rm" field.
|
Operation
CheckFPAdvSIMDEnabled64();
bits(datasize) operand1 = V[n];
bits(datasize) operand2 = V[m];
bits(datasize) result;
bits(esize) element1;
bits(esize) element2;
for e = 0 to elements-1
element1 = Elem[operand1, e, esize];
element2 = Elem[operand2, e, esize];
Elem[result, e, esize] = FPRecipStepFused(element1, element2);
V[d] = result;