[Cyan]<DATools6.0>Core>BitHacksImpl.mesa!3

BitHacksImpl.mesa

Louis Monier December 17, 1985 4:51:55 pm PST

DIRECTORY BitHacks;

BitHacksImpl: CEDAR PROGRAM

EXPORTS BitHacks =

BEGIN

Goodies

-- The arithmetic stuff that people always want

PowersOfTwo: ARRAY [0 .. 33] OF INT = [

1B, 2B, 4B, 1B1, 2B1, 4B1,

1B2, 2B2, 4B2, 1B3, 2B3, 4B3,

1B4, 2B4, 4B4, 1B5, 2B5, 4B5,

1B6, 2B6, 4B6, 1B7, 2B7, 4B7,

1B8, 2B8, 4B8, 1B8, 2B8, 4B8,

1B9, 2B9, 4B9, 1B10];

ODD: PUBLIC PROC [i: INT] RETURNS [BOOL] =

{RETURN [(i MOD 2 # 0)]};

EVEN: PUBLIC PROC [i: INT] RETURNS [BOOL] =

{RETURN [(i MOD 2 = 0)]};

-- Floor

Log2: PUBLIC PROC [n: INT] RETURNS [INT] = {

IF n<=0 THEN RETURN [0];

FOR i: NAT IN [0..33] DO

IF n<PowersOfTwo[i] THEN RETURN [i-1];

REPEAT

FINISHED => ERROR;

ENDLOOP;

};

NBits: PUBLIC PROC [n: INT] RETURNS [INT] = {

IF n<=0 THEN RETURN [0];

IF n=1 THEN RETURN [1];

FOR i: NAT IN [1..33] DO

IF PowersOfTwo[i]>=n THEN RETURN [i];

REPEAT

FINISHED => ERROR;

ENDLOOP;

};

TwoToThe: PUBLIC PROC [x: INT] RETURNS [INT] =

{RETURN[PowersOfTwo[x]]};

TwoToTheLog2: PUBLIC PROC [n: INT] RETURNS [INT] =

{RETURN [TwoToThe[Log2[n]]]};

XthBitOfN: PUBLIC PROC [x, n: INT] RETURNS [BOOL] =

Warning: bit 0 is the LOW order bit (lsb)

{RETURN [IF x<0 THEN FALSE ELSE (n/TwoToThe[x]) MOD 2 =1]};

END.