Originální popis anglicky: 
remquo, remquof, remquol - remainder functions
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
 
 
double remquo(double 
 x, double
  y , int *quo);
 
float remquof(float 
 x, float
  y, int *quo);
 
long double remquol(long double 
 x, long double
   y, int *quo);
 
The 
remquo(), 
remquof(), and 
remquol() functions shall
  compute the same remainder as the 
remainder(), 
remainderf(), and
  
remainderl() functions, respectively. In the object pointed to by
  
quo, they store a value whose sign is the sign of 
x/ 
y
  and whose magnitude is congruent modulo 2 
**n to the magnitude of the
  integral quotient of 
x/ 
y, where 
n is an
  implementation-defined integer greater than or equal to 3.
An application wishing to check for error situations should set 
errno to
  zero and call 
feclearexcept(FE_ALL_EXCEPT) before calling these
  functions. On return, if 
errno is non-zero or
  
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
  non-zero, an error has occurred.
These functions shall return 
x REM 
y.
If 
x or 
y is NaN, a NaN shall be returned.
If 
x is ±Inf or 
y is zero and the other argument is
  non-NaN, a domain error shall occur, and either a NaN (if supported), or an
  implementation-defined value shall be returned.
These functions shall fail if:
  - Domain Error
- The x argument is ±Inf, or the y
      argument is ±0 and the other argument is non-NaN.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
  
errno shall be set to [EDOM]. If the integer expression
  (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid
  floating-point exception shall be raised.
 
The following sections are informative.
None.
On error, the expressions (math_errhandling & MATH_ERRNO) and
  (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
  least one of them must be non-zero.
These functions are intended for implementing argument reductions which can
  exploit a few low-order bits of the quotient. Note that 
x may be so
  large in magnitude relative to 
y that an exact representation of the
  quotient is not practical.
None.
feclearexcept() , 
fetestexcept() , 
remainder() , the Base
  Definitions volume of IEEE Std 1003.1-2001, Section 4.18,
  Treatment of Error Conditions for Mathematical Functions,
  
<math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
  Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
  Operating System Interface (POSIX), The Open Group Base Specifications Issue
  6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
  Engineers, Inc and The Open Group. In the event of any discrepancy between
  this version and the original IEEE and The Open Group Standard, the original
  IEEE and The Open Group Standard is the referee document. The original
  Standard can be obtained online at http://www.opengroup.org/unix/online.html
  .