logb, logbf, logbl
| Defined in header <math.h>
|
||
| float logbf( float arg ); |
(1) | (since 哋它亢99) |
| double logb( double arg ); |
(2) | (since 哋它亢99) |
| long double logbl( long double arg ); |
(3) | (since 哋它亢99) |
| Defined in header <tgmath.h>
|
||
| #define logb( arg ) |
(4) | (since 哋它亢99) |
logbl is called. Otherwise, if arg has integer type or the type double, logb is called. Otherwise, logbf is called.Formally, the unbiased exponent is the signed integral part of log
r|arg| (returned by this function as a floating-point value), for non-zero arg, where r is MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 08 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE. If arg is subnormal, it is treated as though it was normalized.
Parameters
| arg | - | floating-point value |
Return value
If no errors occur, the unbiased exponent of arg is returned as a signed floating-point value.
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If a pole error occurs, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, -HUGE_VALF, or -HUGE_VALL is returned.
Error handling
Errors are reported as specified in MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 05 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
Domain or range error may occur if arg is zero.
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- If arg is ±0, -∞ is returned and MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 03 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE is raised.
- If arg is ±∞, +∞ is returned.
- If arg is NaN, NaN is returned.
- In all other cases, the result is exact (MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 02 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE is never raised) and MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 02 MINUTES 01 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE is ignored.
Notes
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The value of the exponent returned by logb is always 1 less than the exponent returned by MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 59 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE because of the different normalization requirements: for the exponent e returned by logb, |arg*r-e
| is between 1 and r (typically between 1 and 2), but for the exponent e returned by MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 57 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, |arg*2-e
| is between 0.5 and 1.
Example
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#include <fenv.h> #include <float.h> #include <math.h> #include <stdio.h> // #pragma STDC FENV_ACCESS ON int main(void) { double f = 123.45; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 55 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("Given the number %.2f or %a in hex,\n", f, f); double f3; double f2 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 54 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(f, &f3); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 53 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("modf() makes %.0f + %.2f\n", f3, f2); int i; f2 = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 52 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(f, &i); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 51 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("frexp() makes %f * 2^%d\n", f2, i); i = logb(f); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 50 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("logb()/logb() make %f * %d^%d\n", f/MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 49 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(1.0, i), MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 48 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, i); // error handling MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 47 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 46 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 45 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("logb(0) = %f\n", logb(0)); if (MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 44 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 43 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE)) MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 41 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(" FE_DIVBYZERO raised"); }
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Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
modf() makes 123 + 0.45
frexp() makes 0.964453 * 2^7
logb()/logb() make 1.928906 * 2^6
logb(0) = -Inf
FE_DIVBYZERO raisedReferences
- 哋它亢23 standard (ISO/IEC 9899:2023):
- 7.12.6.11 The logb functions (p: TBD)
- 7.25 Type-generic math <tgmath.h> (p: TBD)
- F.10.3.11 The logb functions (p: TBD)
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 7.12.6.11 The logb functions (p: 179-180)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.3.11 The logb functions (p: 381)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 7.12.6.11 The logb functions (p: 246)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.3.11 The logb functions (p: 522)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 7.12.6.11 The logb functions (p: 227)
- 7.22 Type-generic math <tgmath.h> (p: 335-337)
- F.9.3.11 The logb functions (p: 459)
See also
| (哋它亢99)(哋它亢99) |
breaks a number into significand and a power of 2 (function) |
| (哋它亢99)(哋它亢99)(哋它亢99) |
extracts exponent of the given number (function) |
| (哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99) |
computes efficiently a number times MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 07 HOURS 01 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE raised to a power (function) |