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Re: [ft] what's the mean of CEIL( x )?

From: David Turner
Subject: Re: [ft] what's the mean of CEIL( x )?
Date: Fri, 19 May 2006 09:29:48 +0200
User-agent: Thunderbird 1.5 (Windows/20051201)

luoyi a écrit :
sorry, maybe I misunderstand what is "fixed-point 26.6 number".....
can you explain it ?

it means that the value of X can be seen as a 26-bit integer, followed by a 6-bit
fractional part. As in the following graphics:

 |     integer mantissa             | fraction  |
             26 bits                    6 bits
In other words:

 float_value(x) =    (x >> 6) + (x & 63)/64.0

 round(x) = (x+32) & ~63
 floor(x)   = x & ~63
 ceil(x)     = (x+63) & ~63
 int(x)       = (x >> 6)

the macro CEIL(x) as defined really returns int(ceil(x))

note that int(x) is (x >> 6) and *not*   x/64.0 !!

Hope this helps,

- David Turner
- The FreeType Project  (

"David Turner" <address@hidden> ??????:address@hidden
  x=240 corresponds to value 3.75 CEIL(240) => 4

240 / 26.6 =  9.022

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