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Minimal dependency, easy to understand string to floating point number conversion.


  • C compiler with unsigned 64-bit integer type and basic arithmetic on it (comparision, addition, subtraction, bit shifts).
  • <stdint.h> header file or its equivalent defining int32_t, uint32_t, uint64_t types.
  • It is assumed that int type is at least 16-bit wide.
  • Size of other types and system endianess are not important.
  • The C standard library is not required, unless a compiler needs it to provide the above features.
  • No other libraries are required.


  • Converts an ASCII string to IEEE 754 double precision number.
  • Supports scientific notation, all common abbreviations (no zero before dot, ommitted plus signs).
  • The code is easy to understand, algorithm is explained in details.
  • The code is splitted into parser and converter parts, which are independent. Parser is easy to modify to support non-ASCII or wide chars.
  • Parser reads character by character, so can work with pipe style inputs. There is no limit for length of string, string is not buffered.
  • Small in size. On most platforms the compiled code is less than 2 kB.
  • Uses no floating point arithmetic by itself.
  • Covers full range of double precision numbers with precise limit checking.
  • Numbers out of range are converted to infinity with proper sign.
  • Very small numbers are converted to zero with proper sign.


  • No support for explicit "+Inf", "-Inf", "NaN" strings.
  • Denormalized floats are never generated, zero of proper sign is returned instead.
  • The rounding mode is always round towards zero.

Tested platforms

  • Linux on x86_64
  • Linux on x86
  • Linux on ARM
  • Windows on x86_64
  • MorphOS on PowerPC (32-bit)
  • AmigaOS on M68k


No-dependency easy to understand string to floating point number conversion




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