From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/numeric%2Fmath%2Filogb.html | 91 +++++++++++++++++++++++++++++++++++ 1 file changed, 91 insertions(+) create mode 100644 devdocs/c/numeric%2Fmath%2Filogb.html (limited to 'devdocs/c/numeric%2Fmath%2Filogb.html') diff --git a/devdocs/c/numeric%2Fmath%2Filogb.html b/devdocs/c/numeric%2Fmath%2Filogb.html new file mode 100644 index 00000000..75847df0 --- /dev/null +++ b/devdocs/c/numeric%2Fmath%2Filogb.html @@ -0,0 +1,91 @@ +

ilogb, ilogbf, ilogbl

Defined in header <math.h> 
int ilogbf( float arg );
+		 (1) (since C99) 
int ilogb( double arg );
+		 (2) (since C99) 
int ilogbl( long double arg );
+		 (3) (since C99)
Defined in header <tgmath.h> 
#define ilogb( arg )
+		 (4) (since C99)
Defined in header <math.h> 
#define FP_ILOGB0 /*implementation-defined*/
+		 (5) (since C99) 
#define FP_ILOGBNAN /*implementation-defined*/
+		 (6) (since C99)
+1-3) Extracts the value of the unbiased exponent from the floating-point argument arg, and returns it as a signed integer value.
+4) Type-generic macros: If arg has type long double, ilogbl is called. Otherwise, if arg has integer type or the type double, ilogb is called. Otherwise, ilogbf is called.
+5) Expands to integer constant expression whose value is either INT_MIN or -INT_MAX.
+6) Expands to integer constant expression whose value is either INT_MIN or +INT_MAX.

Formally, the unbiased exponent is the integral part of logr|arg| as a signed integral value, for non-zero arg, where r is FLT_RADIX.

+

Parameters

+ +
arg - floating point value

Return value

If no errors occur, the unbiased exponent of arg is returned as a signed int value.

+

If arg is zero, FP_ILOGB0 is returned.

+

If arg is infinite, INT_MAX is returned.

+

If arg is a NaN, FP_ILOGBNAN is returned.

+

If the correct result is greater than INT_MAX or smaller than INT_MIN, the return value is unspecified and a domain error or range error may occur

+

Error handling

Errors are reported as specified in math_errhandling.

+

A domain error or range error may occur if arg is zero, infinite, or NaN.

+

If the correct result is greater than INT_MAX or smaller than INT_MIN, a domain error or a range error may occur

+

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

+

Notes

If arg is not zero, infinite, or NaN, the value returned is exactly equivalent to (int)logb(arg).

+

POSIX requires that a domain error occurs if arg is zero, infinite, NaN, or if the correct result is outside of the range of int.

+

POSIX also requires that, on XSI-conformant systems, the value returned when the correct result is greater than INT_MAX is INT_MAX and the value returned when the correct result is less than INT_MIN is INT_MIN.

+

The correct result can be represented as int on all known implementations. For overflow to occur, INT_MAX must be less than LDBL_MAX_EXP*log2(FLT_RADIX) or INT_MIN must be greater than LDBL_MIN_EXP-LDBL_MANT_DIG)*log2(FLT_RADIX).

+

The value of the exponent returned by ilogb is always 1 less than the exponent retuned by frexp because of the different normalization requirements: for the exponent e returned by ilogb, |arg*r-e| is between 1 and r (typically between 1 and 2), but for the exponent e returned by frexp, |arg*2-e| is between 0.5 and 1.

+

Example

#include <stdio.h>
+#include <math.h>
+#include <float.h>
+#include <fenv.h>
+ 
+#pragma STDC FENV_ACCESS ON
+int main(void)
+{
+    double f = 123.45;
+    printf("Given the number %.2f or %a in hex,\n", f, f);
+ 
+    double f3;
+    double f2 = modf(f, &f3);
+    printf("modf() makes %.0f + %.2f\n", f3, f2);
+ 
+    int i;
+    f2 = frexp(f, &i);
+    printf("frexp() makes %f * 2^%d\n", f2, i);
+ 
+    i = ilogb(f);
+    printf("logb()/ilogb() make %f * %d^%d\n", f/scalbn(1.0, i), FLT_RADIX, i);
+ 
+    // error handling
+    feclearexcept(FE_ALL_EXCEPT);
+    printf("ilogb(0) = %d\n", ilogb(0));
+    if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
+}

Possible output:

+
Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
+modf() makes 123 + 0.45
+frexp() makes 0.964453 * 2^7
+logb()/ilogb() make 1.92891 * 2^6
+ilogb(0) = -2147483648
+    FE_INVALID raised

References

See also

+ + + +
+
(C99)(C99)
 breaks a number into significand and a power of 2
(function)
+
(C99)(C99)(C99)
 extracts exponent of the given number
(function)
+
(C99)(C99)(C99)(C99)(C99)(C99)
 computes efficiently a number times FLT_RADIX raised to a power
(function)
C++ documentation for ilogb
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/numeric/math/ilogb +

+
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