2012-10-02  Robert Dewar  <dewar@adacore.com>

	* s-bignum.adb (Big_Exp): 0**0 should be 1, not 0.
	(Big_Exp): Fix possible error for (-1)**0.
	(Big_Exp): Fix error in computing 2**K for small K.
	(Big_Mod): Fix wrong sign for negative operands.
	(Div_Rem): Fix bad results for operands close to 2**63.
	* s-bignum.ads: Add documentation and an assertion to require
	LLI size to be 64 bits.
	* sem_prag.adb (Analyze_Pragma, case Overflow_Checks): Do not
	allow ELIMINATED if LLI'Size is other than 64 bits.
	* switch-c.adb (Scan_Switches): Do not allow -gnato3 if LLI'Size
	is not 64 bits.
	* switch.ads (Bad_Switch): Add missing pragma No_Return.
	* gnat_ugn.texi: Added appendix on Overflow Check Handling in GNAT.

2012-10-02  Robert Dewar  <dewar@adacore.com>

	* sem_type.adb: Minor reformatting.

From-SVN: r191979