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Kirill Smelkov
go123
Commits
2578d583
Commit
2578d583
authored
Sep 11, 2017
by
Kirill Smelkov
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xmath += CeilLog2, FloorLog2
CeilLog2(x) = min i: 2^i >= x FloorLog2(x) = max i: 2^i <= x
parent
8e6e163f
Changes
2
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2 changed files
with
80 additions
and
29 deletions
+80
-29
xmath/math19.go
xmath/math19.go
+25
-0
xmath/math_test.go
xmath/math_test.go
+55
-29
No files found.
xmath/math19.go
View file @
2578d583
...
...
@@ -34,5 +34,30 @@ func CeilPow2(x uint64) uint64 {
}
}
// CeilLog2 returns minimal i: 2^i >= x
func
CeilLog2
(
x
uint64
)
int
{
switch
bits
.
OnesCount64
(
x
)
{
case
0
:
return
0
case
1
:
return
bits
.
Len64
(
x
)
-
1
default
:
return
bits
.
Len64
(
x
)
}
}
// FloorLog2 returns maximal i: 2^i <= x
//
// x=0 gives -> -1.
func
FloorLog2
(
x
uint64
)
int
{
switch
bits
.
OnesCount64
(
x
)
{
case
0
:
return
-
1
default
:
return
bits
.
Len64
(
x
)
-
1
}
}
// XXX if needed: NextPow2 (y > x, such that y = 2^i) is
// 1 << bits.Len64(x)
xmath/math_test.go
View file @
2578d583
...
...
@@ -21,38 +21,64 @@ import (
"testing"
)
func
Test
Ceil
Pow2
(
t
*
testing
.
T
)
{
testv
:=
[]
struct
{
in
,
out
uint64
}
{
{
0
,
0
},
{
1
,
1
},
{
2
,
2
},
{
3
,
4
},
{
4
,
4
},
{
5
,
8
},
{
5
,
8
},
{
6
,
8
},
{
7
,
8
},
{
8
,
8
},
{
9
,
16
},
{
10
,
16
},
{
11
,
16
},
{
12
,
16
},
{
13
,
16
},
{
14
,
16
},
{
15
,
16
},
{
16
,
16
},
{
1
<<
62
-
1
,
1
<<
62
},
{
1
<<
62
,
1
<<
62
},
{
1
<<
62
+
1
,
1
<<
63
},
{
1
<<
63
-
1
,
1
<<
63
},
{
1
<<
63
,
1
<<
63
},
func
TestPow2
(
t
*
testing
.
T
)
{
testv
:=
[]
struct
{
x
,
xcpow2
uint64
;
xclog2
int
}
{
{
0
,
0
,
0
},
{
1
,
1
,
0
},
{
2
,
2
,
1
},
{
3
,
4
,
2
},
{
4
,
4
,
2
},
{
5
,
8
,
3
},
{
5
,
8
,
3
},
{
6
,
8
,
3
},
{
7
,
8
,
3
},
{
8
,
8
,
3
},
{
9
,
16
,
4
},
{
10
,
16
,
4
},
{
11
,
16
,
4
},
{
12
,
16
,
4
},
{
13
,
16
,
4
},
{
14
,
16
,
4
},
{
15
,
16
,
4
},
{
16
,
16
,
4
},
{
1
<<
62
-
1
,
1
<<
62
,
62
},
{
1
<<
62
,
1
<<
62
,
62
},
{
1
<<
62
+
1
,
1
<<
63
,
63
},
{
1
<<
63
-
1
,
1
<<
63
,
63
},
{
1
<<
63
,
1
<<
63
,
63
},
}
for
_
,
tt
:=
range
testv
{
out
:=
CeilPow2
(
tt
.
in
)
if
out
!=
tt
.
out
{
t
.
Errorf
(
"CeilPow2(%v) -> %v ; want %v"
,
tt
.
in
,
out
,
tt
.
out
)
xcpow2
:=
CeilPow2
(
tt
.
x
)
if
xcpow2
!=
tt
.
xcpow2
{
t
.
Errorf
(
"CeilPow2(%v) -> %v ; want %v"
,
tt
.
x
,
xcpow2
,
tt
.
xcpow2
)
}
xclog2
:=
CeilLog2
(
tt
.
xcpow2
)
if
xclog2
!=
tt
.
xclog2
{
t
.
Errorf
(
"CeilLog2(%v) -> %v ; want %v"
,
tt
.
xcpow2
,
xclog2
,
tt
.
xclog2
)
}
}
xclog2
=
CeilLog2
(
tt
.
x
)
if
xclog2
!=
tt
.
xclog2
{
t
.
Errorf
(
"CeilLog2(%v) -> %v ; want %v"
,
tt
.
x
,
xclog2
,
tt
.
xclog2
)
}
xflog2
:=
FloorLog2
(
tt
.
xcpow2
)
xflog2Ok
:=
tt
.
xclog2
if
tt
.
x
==
0
{
xflog2Ok
=
-
1
}
if
xflog2
!=
xflog2Ok
{
t
.
Errorf
(
"FloorLog2(%v) -> %v ; want %v"
,
tt
.
xcpow2
,
xflog2
,
xflog2Ok
)
}
if
tt
.
x
!=
tt
.
xcpow2
{
xflog2Ok
--
}
xflog2
=
FloorLog2
(
tt
.
x
)
if
xflog2
!=
xflog2Ok
{
t
.
Errorf
(
"FloorLog2(%v) -> %v ; want %v"
,
tt
.
x
,
xflog2
,
xflog2Ok
)
}
}
}
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