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.
Green
True
True
True
0
1
1
0
0
1
0
1
0
0
0
1
1
0
1
0
1
FLOGB <Zd>.<T>, <Pg>/M, <Zn>.<T>
if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then UNDEFINED;
if size == '00' then UNDEFINED;
constant integer esize = 8 << UInt(size);
constant integer g = UInt(Pg);
constant integer n = UInt(Zn);
constant integer d = UInt(Zd);
<Zd>
Is the name of the destination scalable vector register, encoded in the "Zd" field.
<T>
Is the size specifier,
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.
CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = P[g, PL];
constant bits(VL) operand = if AnyActiveElement(mask, esize) then Z[n, VL] else Zeros(VL);
bits(VL) result = Z[d, VL];
for e = 0 to elements-1
if ActivePredicateElement(mask, e, esize) then
constant bits(esize) element = Elem[operand, e, esize];
Elem[result, e, esize] = FPLogB(element, FPCR);
Z[d, VL] = result;