FLOGB

Floating-point base 2 logarithm as integer.

This instruction returns the signed integer base 2 logarithm of each floating-point input element |x| after normalization.

This is the unbiased exponent of x used in the representation of the floating-point value, such that, for positive x, x = significand × 2exponent.

The integer results are placed in elements of the destination vector which have the same width (esize) as the floating-point input elements:

* If x is normal, the result is the base 2 logarithm of x.

* If x is subnormal, the result corresponds to the normalized representation.

* If x is infinite, the result is 2(esize-1)-1.

* If x is ±0.0 or NaN, the result is -2(esize-1).

Inactive elements in the destination vector register remain unmodified.

313029282726252423222120191817161514131211109876543210
0110010100011size0101PgZnZd

SVE2

FLOGB <Zd>.<T>, <Pg>/M, <Zn>.<T>

if !HaveSVE2() then UNDEFINED; if size == '00' then UNDEFINED; integer esize = 8 << UInt(size); integer g = UInt(Pg); integer n = UInt(Zn); integer d = UInt(Zd);

Assembler Symbols

<Zd>

Is the name of the destination scalable vector register, encoded in the "Zd" field.

<T> Is the size specifier, encoded in size:
size <T>
00 RESERVED
01 H
10 S
11 D
<Pg>

Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Zn>

Is the name of the source scalable vector register, encoded in the "Zn" field.

Operation

CheckSVEEnabled(); integer elements = VL DIV esize; bits(PL) mask = P[g]; bits(VL) operand = Z[n]; bits(VL) result = Z[d]; for e = 0 to elements-1 bits(esize) element = Elem[operand, e, esize]; if ElemP[mask, e, esize] == '1' then Elem[result, e, esize] = FPLogB(element, FPCR); Z[d] = result;

Operational information

This instruction might be immediately preceded in program order by a MOVPRFX instruction that conforms to all of the following requirements, otherwise the behavior of either or both instructions is unpredictable:

The MOVPRFX instructions that can be used with this instruction are as follows:


Internal version only: isa v30.44, AdvSIMD v27.08, pseudocode v8.5-2019-06_rc2-5-g22901f2, sve v2019-06_rc4 ; Build timestamp: 2019-06-26T22:30

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