The results below can only give a rough estimate of the resources necessary for using certain library functions. There is a number of factors which can both increase or reduce the effort required:

Expenses for preparation of operands and their stack are not considered.

In the table, the size includes all additional functions (for example, function to multiply two integers) but they are only linked from the library.

Expenses of time of performance of some functions essentially depend on parameters of a call, for example, qsort() is recursive, and sprintf() receives parameters in a stack.

Different versions of the compiler can give a significant difference in code size and execution time. For example, the dtostre() function, compiled with avr-gcc 3.4.6, requires 930 bytes. After transition to avr-gcc 4.2.3, the size become 1088 bytes.

A few of libc functions.

Avr-gcc version is 4.2.3

The size of function is given in view of all picked up functions. By default Avr-libc is compiled with -mcall-prologues option. In brackets the size without taking into account modules of a prologue and an epilogue is resulted. Both of the size can coincide, if function does not cause a prologue/epilogue.

Function	Units	Avr2	Avr25	Avr4
atoi ("12345")	Flash bytes Stack bytes MCU clocks	82 (82) 2 155	78 (78)	74 (74) 2 149
atol ("12345")	Flash bytes Stack bytes MCU clocks	122 (122) 2 221	118 (118)	118 (118) 2 219
dtostre (1.2345, s, 6, 0)	Flash bytes Stack bytes MCU clocks	1184 (1072) 17 1313	1088 (978)	1088 (978) 17 1152
dtostrf (1.2345, 15, 6, s)	Flash bytes Stack bytes MCU clocks	1676 (1564) 36 1608	1548 (1438)	1548 (1438) 36 1443
itoa (12345, s, 10)	Flash bytes Stack bytes MCU clocks	150 (150) 4 1172	134 (134)	134 (134) 4 1152
ltoa (12345L, s, 10)	Flash bytes Stack bytes MCU clocks	220 (220) 9 3174	200 (200)	200 (200) 9 3136
malloc (1)	Flash bytes Stack bytes MCU clocks	554 (554) 4 196	506 (506)	506 (506) 4 178
realloc ((void *)0, 1)	Flash bytes Stack bytes MCU clocks	1152 (1040) 20 303	1042 (932)	1042 (932) 20 280
qsort (s, sizeof(s), 1, cmp)	Flash bytes Stack bytes MCU clocks	1242 (1130) 38 20914	990 (880)	1008 (898) 38 16678
sprintf_min (s, "%d", 12345)	Flash bytes Stack bytes MCU clocks	1216 (1104) 59 1846	1090 (980)	1086 (976) 59 1711
sprintf (s, "%d", 12345)	Flash bytes Stack bytes MCU clocks	1674 (1562) 58 1610	1542 (1432)	1498 (1388) 58 1528
sprintf_flt (s, "%e", 1.2345)	Flash bytes Stack bytes MCU clocks	3334 (3222) 66 2513	3084 (2974)	3040 (2930) 66 2297
sscanf_min ("12345", "%d", &i)	Flash bytes Stack bytes MCU clocks	1540 (1428) 55 1339	1354 (1244)	1354 (1244) 55 1240
sscanf ("12345", "%d", &i)	Flash bytes Stack bytes MCU clocks	1950 (1838) 53 1334	1704 (1594)	1704 (1594) 53 1235
sscanf ("point,color", "%[a-z]", s)	Flash bytes Stack bytes MCU clocks	1950 (1838) 87 2878	1704 (1594)	1704 (1594) 87 2718
sscanf_flt ("1.2345", "%e", &x)	Flash bytes Stack bytes MCU clocks	3298 (3186) 63 2187	2934 (2824)	2918 (2808) 63 1833
strtod ("1.2345", &p)	Flash bytes Stack bytes MCU clocks	1570 (1458) 22 1237	1472 (1362)	1456 (1346) 22 971
strtol ("12345", &p, 0)	Flash bytes Stack bytes MCU clocks	942 (830) 29 1074	874 (764)	808 (698) 21 722

Math functions.

The table contains the number of MCU clocks to calculate a function with a given argument(s). The main reason of a big difference between Avr2 and Avr4 is a hardware multiplication.

Function	Avr2	Avr4
__addsf3 (1.234, 5.678)	113	108
__mulsf3 (1.234, 5.678)	375	138
__divsf3 (1.234, 5.678)	466	465
acos (0.54321)	4411	2455
asin (0.54321)	4517	2556
atan (0.54321)	4710	2271
atan2 (1.234, 5.678)	5270	2857
cbrt (1.2345)	2684	2555
ceil (1.2345)	177	177
cos (1.2345)	3387	1671
cosh (1.2345)	4922	2979
exp (1.2345)	4708	2765
fdim (5.678, 1.234)	111	111
floor (1.2345)	180	180
fmax (1.234, 5.678)	39	37
fmin (1.234, 5.678)	35	35
fmod (5.678, 1.234)	131	131
frexp (1.2345, 0)	42	41
hypot (1.234, 5.678)	1341	866
ldexp (1.2345, 6)	42	42
log (1.2345)	4142	2134
log10 (1.2345)	4498	2260
modf (1.2345, 0)	433	429
pow (1.234, 5.678)	9293	5047
round (1.2345)	150	150
sin (1.2345)	3353	1653
sinh (1.2345)	4946	3003
sqrt (1.2345)	494	492
tan (1.2345)	4381	2426
tanh (1.2345)	5126	3173
trunc (1.2345)	178	178