ESP8266_RTOS_SDK/components/newlib

The newlib version has been updated to "2.2.0" and supply two version C libraries to user. One is "libc.a" which functions have more features base on stand C, another is "libc_nano.c" which functions have less function.

You can choose the one you needed by menuconfig:

Component config --->
        newlib --- >
                newlib level(XXXX)
                        ( ) normal
                        ( ) nano

The normal "libc" has position argument, "long long" type data and float data transformation at function printf/scanf and so on. So it should cost more stack and heap, the test data as following:

	Object		Origin newlib				New newlib				New newlib nano
			Start heap/byte	53000			Start heap/byte	49184			Start heap/byte		51824
	Fucntion		Stack/byte	Heap/byte	Heap cost/byte		Stack/byte	Heap/byte	Heap cost/byte		Stack/byte	Heap/byte	Heap cost/byte
	isalnum		96	53000	0		80	49184	0		80	51824	0
	isalpha		80	53000	0		64	49184	0		64	51824	0
	isspace		80	53000	0		64	49184	0		64	51824	0
	atoi		160	53000	0		144	49184	0		144	51824	0
	strtol		144	53000	0		128	49184	0		128	51824	0
	atof		224	53000	0		208	49184	0		208	51824	0
	atoff		224	53000	0		208	49184	0		208	51824	0
	strtod		208	53000	0		192	49184	0		192	51824	0
	strtof		208	53000	0		192	49184	0		192	51824	0
	asprintf		880	52616	384		1200	48800	384		608	51632	192
	sscanf		1552	53000	0		2032	49184	0		1120	51824	0
	gmtime		944	52616	384		1040	48576	608		1296	51512	312
	localtime		160	53000	0		288	49184	0		288	51824	0
	mktime		320	53000	0		448	49184	0		448	51824	0
	asctime		768	52488	480		1264	48528	656		752	51464	360
	settimeofday		336	53000	0		320	49184	0		320	51824	0
	gettimeofday		480	53000	0		464	49184	0		464	51824	0
	localtime_r		304	53000	0		432	49184	0		432	51824	0
	asprintf（64bit）		752	52424	576		1136	48336	848		608	51272	552
	sscanf（64bit）		1056	53000	0		1376	49184	0		1040	51824	0