Floating point bug when writing to file in Matlab? -

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im not sure if im missing simple following code fails (a , b meant same):

a=single(2147483584) f=fopen('test','wb'); fwrite(f,a,'int32') fclose(f);  f=fopen('test','rb'); b=fread(f,inf,'int32'); fclose(f) b

with output:

a =     2.1475e+009 b =    -2.1475e+009

and following code succeeds:

a=single(2147483583) f=fopen('test','wb'); fwrite(f,a,'int32') fclose(f);  f=fopen('test','rb'); b=fread(f,inf,'int32'); fclose(f) b

with output:

a =     2.1475e+009 b =    2.1475e+009

does know why?

i don't know matlab well, seems clear what's happening here. you're converting a float , storing result of conversion 32-bit signed integer. nearest single-precision ieee 754 float integer 2147483584 2147483648.0, or 2**31. 32-bit integer can represent values in range [-2**31, 2**31-1], looks though when write value integer, gets wrapped modulo 2**32 give -2**31 instead of 2**31.

in contrast, nearest single-precision float 2147483583 2147483520.0, does fit in 32-bit integer.


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