Some of the various resources that I've found useful for implementing the standard C library.

Books

• The C Programming Language, 2nd Edition

  Also known as "K&R", this is a must-have text for a C programmer. It's a nice and quick overview of the C language.

• The Standard C Library

  A complete text on implementing and using the standard C library.

• Secure Coding in C and C++, 2nd Edition

  A very thorough look at common security flaws in C and C++ programs, how they are exploited, and mitigations for them.

• The CERT C Coding Standard, 2nd Edition

  A more succinct version of the "Secure Coding in C and C++" book. Lists rules along with examples of conforming and non-conforming code.

Websites

• SEI CERT C Coding Standard

  Website with the contents of the "CERT C Coding Standard" book which is actively updated.

• What Every Computer Scientist Should Know About Floating-Point Arithmetic

  A fantastic paper which goes into extreme detail on floating-point arithmetic.

• C Reference Manual

  This was the C standard before one existed.

Standards

• ISO/IEC 9899:1990

  The version of the C standard being implemented by welibc.

• ANSI C89 Draft

  A free draft version of C89.

• System V x86_64 ABI

  Defines the interface between the operating system and the x86_64 architecture.

• IEEE 754-2008

  The IEEE Standard for Floating-Point Arithmetic.