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%2Fldexp.html | 79 +++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100644 devdocs/c/numeric%2Fmath%2Fldexp.html (limited to 'devdocs/c/numeric%2Fmath%2Fldexp.html') diff --git a/devdocs/c/numeric%2Fmath%2Fldexp.html b/devdocs/c/numeric%2Fmath%2Fldexp.html new file mode 100644 index 00000000..b2e09059 --- /dev/null +++ b/devdocs/c/numeric%2Fmath%2Fldexp.html @@ -0,0 +1,79 @@ +

ldexp, ldexpf, ldexpl

Defined in header <math.h> 
float       ldexpf( float arg, int exp );
+		 (1) (since C99) 
double      ldexp( double arg, int exp );
+		 (2) 
long double ldexpl( long double arg, int exp );
+		 (3) (since C99)
Defined in header <tgmath.h> 
#define ldexp( arg, exp )
+		 (4) (since C99)
+1-3) Multiplies a floating point value arg by the number 2 raised to the exp power.
+4) Type-generic macro: If arg has type long double, ldexpl is called. Otherwise, if arg has integer type or the type double, ldexp is called. Otherwise, ldexpf is called, respectively.

Parameters

+ + +
arg - floating point value
exp - integer value

Return value

If no errors occur, arg multiplied by 2 to the power of exp (arg×2exp) is returned.

+

If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.

+

If a range error due to underflow occurs, the correct result (after rounding) is returned.

+

Error handling

Errors are reported as specified in math_errhandling.

+

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

+

Notes

On binary systems (where FLT_RADIX is 2), ldexp is equivalent to scalbn.

+

The function ldexp ("load exponent"), together with its dual, frexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.

+

On many implementations, ldexp is less efficient than multiplication or division by a power of two using arithmetic operators.

+

Example

#include <stdio.h>
+#include <math.h>
+#include <float.h>
+#include <errno.h>
+#include <fenv.h>
+#pragma STDC FENV_ACCESS ON
+int main(void)
+{
+    printf("ldexp(7, -4) = %f\n", ldexp(7, -4));
+    printf("ldexp(1, -1074) = %g (minimum positive subnormal double)\n",
+            ldexp(1, -1074));
+    printf("ldexp(nextafter(1,0), 1024) = %g (largest finite double)\n",
+            ldexp(nextafter(1,0), 1024));
+    // special values
+    printf("ldexp(-0, 10) = %f\n", ldexp(-0.0, 10));
+    printf("ldexp(-Inf, -1) = %f\n", ldexp(-INFINITY, -1));
+    //error handling
+    errno = 0; feclearexcept(FE_ALL_EXCEPT);
+    printf("ldexp(1, 1024) = %f\n", ldexp(1, 1024));
+    if(errno == ERANGE) perror("    errno == ERANGE");
+    if(fetestexcept(FE_OVERFLOW)) puts("    FE_OVERFLOW raised");
+}

Possible output:

+
ldexp(7, -4) = 0.437500
+ldexp(1, -1074) = 4.94066e-324 (minimum positive subnormal double)
+ldexp(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)
+ldexp(-0, 10) = -0.000000
+ldexp(-Inf, -1) = -inf
+ldexp(1, 1024) = inf
+    errno == ERANGE: Numerical result out of range
+    FE_OVERFLOW raised

References

See also

+ + +
+
(C99)(C99)
 breaks a number into significand and a power of 2
(function)
+
(C99)(C99)(C99)(C99)(C99)(C99)
 computes efficiently a number times FLT_RADIX raised to a power
(function)
C++ documentation for ldexp
+

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

+
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