base64

Searching the web for a C/C++ base64 implementation yields many results. The first hit as of 2016-12-10 for "c++ base64" are:

• http://www.adp-gmbh.ch/cpp/common/base64.html (René Nyffenegger's implementation which is often quoted by other implementations)
• http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c which is a stackoverflow entry with multiple "here is my implementation which I think is better"
• http://stackoverflow.com/questions/342409/how-do-i-base64-encode-decode-in-c which holds more code snippets
• http://libb64.sourceforge.net/ which is an opensource implementation claiming to be fast

Looking further, we find many more:

• http://web.mit.edu/freebsd/head/contrib/wpa/src/utils/base64.c from Jouni Malinen under BSD license
• https://en.wikibooks.org/wiki/Algorithm_Implementation/Miscellaneous/Base64 has both a C and C++ implementations

How does one chose? This project aims at collecting and comparing the different implementations available.

Feel free to improve this test or to submit new implementations!

Disclaimer

Keep in mind that some implementations were slightly modified to have a common interface for the test framework. In all cases, line breaks were omitted both for encoding and parsing. Also, although all implementates have been unit-tested, no analysis whatsoever has been made on error handling, so some slower implementation may actually be better at reporting malformed base64 strings for instance.

I do not own any of these implementations - make sure you check their respective license before using them.

Compared implementations

adp-gmbh (René Nyffenegger)

From http://www.adp-gmbh.ch/cpp/common/base64.html

lib64

From https://sourceforge.net/projects/libb64/

libcurl

From https://curl.haxx.se/libcurl/

Internet Software Consortium

From https://opensource.apple.com/source/basic_cmds/basic_cmds-55/uuencode/base64.c

Arduino-Base64

From https://github.com/adamvr/arduino-base64 from BuLogic's fork (https://github.com/BuLogics/libb64)

LihO

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

Manuel Martinez

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

DaedalusAlpha

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

Elegant Dice

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

polfosol

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

omnifarious

From stackoverflow thread at http://stackoverflow.com/questions/5288076/doing-base64-encoding-and-decoding-in-openssl-c

** Note that although this implementation is in the results, it does not produce valid results - including extra '=' padding when not necessary.

user152949

From stackoverflow thread at http://stackoverflow.com/questions/180947/base64-decode-snippet-in-c

jounimalinen

From http://web.mit.edu/freebsd/head/contrib/wpa/src/utils/base64.c

test_wikibooks_org_c

From https://en.wikibooks.org/wiki/Algorithm_Implementation/Miscellaneous/Base64

test_wikibooks_org_cpp

From https://en.wikibooks.org/wiki/Algorithm_Implementation/Miscellaneous/Base64

apache

Which I think was based on Rob McCool's uuencode's implementation in 1993 https://opensource.apple.com/source/QuickTimeStreamingServer/QuickTimeStreamingServer-452/CommonUtilitiesLib/base64.c

NibbleAndAHalf

From https://github.com/superwills/NibbleAndAHalf/

Gnome

From https://github.com/GNOME/glib/blob/master/glib/gbase64.c

cppcodec

From https://github.com/tplgy/cppcodec

Results for Encoding (32bit Visual Studio 2015)

The table below shows the number of microseconds for the encoding of different buffer sizes:

Implementation	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63	64	68	72	76	80	96	112	128	160	192	224	256
apache	0.107272	0.109874	0.108418	0.112368	0.113487	0.112324	0.114798	0.114436	0.112879	0.198983	0.199052	0.203594	0.2053	0.206689	0.206527	0.207957	0.208973	0.207636	0.209693	0.211857	0.211648	0.210322	0.208795	0.209596	0.209342	0.213156	0.210805	0.213986	0.215526	0.215007	0.216999	0.2212	0.22374	0.224083	0.22553	0.223034	0.224299	0.221733	0.221059	0.224744	0.224981	0.226101	0.224896	0.232075	0.229934	0.232761	0.230755	0.229771	0.233281	0.232544	0.232631	0.240381	0.241165	0.239635	0.241833	0.246243	0.240364	0.242389	0.242162	0.243953	0.250475	0.24564	0.244032	0.243186	0.24911	0.261442	0.260752	0.263289	0.282692	0.291384	0.312266	0.32686	0.354342	0.391914	0.411585
jounimalinen	0.116945	0.120135	0.119827	0.124533	0.126961	0.123922	0.12556	0.126944	0.126419	0.207953	0.205896	0.213323	0.210704	0.209417	0.208586	0.209985	0.211231	0.211595	0.213811	0.214522	0.21624	0.216002	0.218284	0.22159	0.22397	0.224979	0.22036	0.221201	0.225282	0.220686	0.221162	0.225916	0.225883	0.226214	0.224841	0.226839	0.230714	0.230809	0.227632	0.232252	0.238526	0.237746	0.231971	0.231042	0.233279	0.236185	0.235507	0.238087	0.238205	0.243735	0.242036	0.241123	0.243045	0.24066	0.245986	0.247064	0.246648	0.250238	0.249466	0.249547	0.250626	0.253014	0.254703	0.254835	0.256435	0.257322	0.273092	0.275612	0.292918	0.303408	0.322363	0.344941	0.378558	0.419151	0.434379
NibbleAndAHalf	0.116597	0.115518	0.116778	0.122256	0.124338	0.12235	0.124425	0.126561	0.129946	0.215682	0.210449	0.215203	0.217577	0.214509	0.213927	0.217072	0.214548	0.217736	0.221573	0.222749	0.22543	0.229612	0.228851	0.234062	0.234331	0.235352	0.238474	0.236259	0.236497	0.239138	0.238925	0.243109	0.245422	0.239948	0.239373	0.244023	0.246597	0.24283	0.249269	0.246636	0.246226	0.251916	0.249464	0.251701	0.257879	0.256856	0.25581	0.258465	0.266965	0.25881	0.263202	0.259383	0.266259	0.270631	0.270189	0.272725	0.271879	0.271732	0.276799	0.281525	0.276441	0.275447	0.278408	0.276491	0.289264	0.289141	0.298731	0.310245	0.332917	0.35224	0.383732	0.422086	0.462272	0.512932	0.545165
internetsoftwareconsortium	0.115257	0.116053	0.110223	0.121342	0.12098	0.11864	0.124815	0.125146	0.121998	0.219368	0.220235	0.212528	0.217972	0.223357	0.216643	0.229876	0.232764	0.224849	0.230955	1.3659	0.226677	0.233913	0.235012	0.230633	0.23975	0.241266	0.235514	0.242964	0.247031	0.238508	0.249469	0.249177	0.245128	0.255171	0.259358	0.25184	0.260118	0.25817	0.258838	0.273057	0.275565	0.265996	0.274125	0.271166	0.267186	0.271759	0.27407	0.268134	0.282066	0.286918	0.282079	0.287813	0.286647	0.286338	0.295869	0.295616	0.291061	0.301998	0.301387	0.291685	0.300873	0.306202	0.299857	0.304343	0.316577	0.31418	0.330376	0.331954	0.3611	0.382843	0.415684	0.477251	0.522291	0.607917	0.636043
polfosol	0.101834	0.103146	0.104478	0.107201	0.110477	0.109419	0.113974	0.115238	0.114783	0.205934	0.206937	0.205245	0.210234	0.21737	0.214958	0.22149	0.216415	0.217571	0.219057	0.222633	0.219874	0.225758	0.226981	0.229861	0.234125	0.238059	0.234311	0.240252	0.23594	0.23903	0.241235	0.241743	0.240367	0.244349	0.24889	0.254705	0.260901	0.257649	0.25867	0.259463	0.263679	0.260268	0.265119	0.264819	0.271856	0.268498	0.275229	0.273136	0.282904	0.281921	0.272918	0.27631	0.279243	0.284727	0.281549	0.291418	0.288264	0.293761	0.289888	0.295814	0.299102	0.303185	0.303025	0.307904	0.317427	0.323714	0.335027	0.335647	0.366696	0.397239	0.429128	0.494767	0.549747	0.600015	0.652053
wikibooks_org_c	0.111841	0.11237	0.113272	0.118199	0.119268	0.118687	0.124072	0.123435	0.12354	0.213497	0.216511	0.214886	0.222639	0.219644	0.22355	0.229885	0.228831	0.227117	0.23303	0.234915	0.234665	0.242299	0.241615	0.242747	0.246547	0.246222	0.246517	0.248375	0.251941	0.249905	0.254262	0.257238	0.25699	0.26116	0.261516	0.262206	0.267327	0.268851	0.269359	0.273196	0.271578	0.273941	0.283005	0.279922	0.278093	0.285581	0.282363	0.284521	0.288021	0.289664	0.287732	0.293018	0.294559	0.293199	0.302892	0.298181	0.301506	0.304814	0.309547	0.311768	0.310959	0.310851	0.313062	0.31872	0.324646	0.330979	0.344607	0.345094	0.379339	0.4151	0.446048	0.513498	0.570684	0.636349	0.701049
gnome	0.135533	0.133178	0.136323	0.141088	0.142301	0.140361	0.146863	0.149798	0.237919	0.325182	0.323265	0.326513	0.353908	0.34468	0.343271	0.351908	0.347984	0.37542	0.393741	0.358943	0.365761	0.390206	0.380117	0.367369	0.372321	0.383602	0.380668	0.392568	0.386307	0.38475	0.390319	0.388613	0.387994	0.401119	0.391747	0.393943	0.394962	0.394429	0.394188	0.40599	0.404921	0.404345	0.412851	0.409566	0.405893	0.420956	0.413478	0.412663	0.424123	0.425969	0.424524	0.434929	0.492733	0.440431	0.447185	0.445682	0.439731	0.502783	0.506347	0.485935	0.497747	0.460965	0.462629	0.467165	0.470323	0.482962	0.496583	0.520713	0.563158	0.614627	0.644528	0.734544	0.766645	0.838784	0.887723
arduino	0.118509	0.119117	0.122076	0.132471	0.135852	0.137738	0.147221	0.149313	0.150027	0.248766	0.250231	0.249989	0.255977	0.260937	0.259267	0.27324	0.285361	0.287799	0.303425	0.302549	0.293454	0.304654	0.307849	0.306079	0.311677	0.313761	0.319655	0.329641	0.327105	0.332071	0.339899	0.346803	0.354286	0.357898	0.355284	0.358658	0.371691	0.382168	0.374741	0.38412	0.388211	0.392743	0.399104	0.399688	0.399034	0.411836	0.421092	0.411182	0.433069	0.428812	0.434977	0.440116	0.446257	0.445337	0.456127	0.462041	0.461325	0.476475	0.476183	0.475551	0.484894	0.487741	0.487755	0.505399	0.514935	0.53055	0.551778	0.575863	0.645695	0.728413	0.802685	0.960458	1.0898	1.25342	1.38764
elegantdice	0.120279	0.117399	0.114282	0.128019	0.125479	0.124204	0.141976	0.141571	0.139255	0.239164	0.239079	0.235926	0.253402	0.258426	0.254803	0.265197	0.264855	0.26281	0.28161	0.276692	0.274925	0.291926	0.289096	0.287456	0.303269	0.30384	0.310483	0.329711	0.324584	0.322671	0.341857	0.336035	0.335683	0.350838	0.353414	0.347747	0.365522	0.372094	0.362902	0.374118	0.380939	0.370515	0.386478	0.386998	0.382921	0.398647	0.392852	0.403361	0.416809	0.419743	0.417849	0.424565	0.427383	0.431703	0.43796	0.434931	0.435994	0.461213	0.453942	0.455581	0.472892	0.469043	0.471474	0.489294	0.489363	0.511759	0.544592	0.546474	0.636146	0.71266	0.793598	0.916679	1.04726	1.22271	1.39193
daedalusalpha	0.116234	0.116886	0.116678	0.125134	0.125061	0.12768	0.139621	0.137369	0.141683	0.244265	0.246068	0.244841	0.259849	0.258451	0.261099	0.278403	0.27343	0.276961	0.284333	0.283911	0.284893	0.29776	0.298132	0.298584	0.307636	0.307478	0.316421	0.331374	0.327825	0.329681	0.33903	0.338558	0.344509	0.347761	0.341977	0.351996	0.365871	0.3662	0.369573	0.379255	0.381402	0.376258	0.390387	0.39532	0.394264	0.405287	0.402868	0.404522	0.417034	0.418428	0.411923	0.429833	0.425251	0.426483	0.438304	0.439262	0.435069	0.447554	0.450935	0.463644	0.475204	0.469073	0.468742	0.480038	0.488784	0.510492	0.535589	0.536782	0.632651	0.702791	0.800494	0.923296	1.07088	1.21836	1.39385
CppCodec	0.15069	0.158567	0.138497	0.168342	0.166635	0.153346	0.186204	0.188177	0.171308	0.282119	0.282008	0.266554	0.294051	0.300822	0.286171	0.32079	0.325976	0.304998	0.338276	0.340245	0.322298	0.360409	0.359788	0.34343	0.378849	0.376986	0.364181	0.401775	0.402895	0.386545	0.42042	0.425553	0.403445	0.426847	0.437581	0.407885	0.442607	0.45072	0.427876	0.456889	0.466088	0.437493	0.470103	0.481163	0.457022	0.488841	0.495342	0.473969	0.507449	0.509039	0.492679	0.522791	0.534167	0.514197	0.545029	0.545579	0.522751	0.558023	0.557688	0.542154	0.571744	0.591842	0.562313	0.597414	0.61631	0.606543	0.66973	0.679971	0.763969	0.881845	0.964839	1.16263	1.30588	1.55547	1.70925
manuelmartinez	0.108172	0.10647	0.110711	0.126003	0.123382	0.124434	0.139173	0.135681	0.13304	0.241411	0.240099	0.242773	0.255605	0.254181	0.264502	0.27774	0.280288	0.282225	0.291553	0.287108	0.286286	0.403327	0.409142	0.439129	0.426305	0.410181	0.408871	0.422964	0.429584	0.433074	0.443868	0.440035	0.440086	0.55854	0.568374	0.563839	0.580749	0.569478	0.570619	0.603095	0.596884	0.593876	0.599073	0.597557	0.599232	0.628666	0.624621	0.618059	0.619371	0.626572	0.630231	0.751164	0.738812	0.734167	0.750632	0.759031	0.757563	0.776913	0.765035	0.76417	0.786586	0.778931	0.822597	0.803996	0.797341	0.807974	0.986816	0.984886	1.04653	1.12319	1.31857	1.48325	1.73524	1.98801	2.10649
wikibooks_org_cpp	0.14271	0.146374	0.145571	0.177607	0.187325	0.184229	0.217976	0.222482	0.222614	0.438053	0.43716	0.435366	0.474087	0.479739	0.479673	0.512877	0.519873	0.520476	1.78637	1.34597	0.558659	0.592123	0.589943	0.596795	0.627187	0.635859	0.634421	0.667261	0.677495	0.674617	0.707459	0.713615	0.725515	0.759847	0.762032	0.767055	0.798947	0.800616	0.806595	0.830645	0.837096	0.83734	0.86312	0.877364	0.886341	0.91131	0.919791	0.921068	0.954667	0.950945	0.958561	0.992891	0.994779	0.996058	1.02685	1.04625	1.03682	1.07072	1.07567	1.08906	1.11381	1.11478	1.12971	1.15198	1.2061	1.25631	1.30908	1.36422	1.55594	1.78958	2.01713	2.4419	2.89068	3.35203	3.74915
libb64	3.17659	3.12883	3.15834	3.15209	3.14258	3.178	3.16715	3.12729	3.12538	3.23839	3.20614	3.27968	3.19132	3.1893	3.24556	3.28203	3.26046	3.23467	3.29694	3.25188	3.29628	3.39604	3.38097	3.39732	3.39032	3.46107	3.43669	3.4446	3.42091	3.39229	3.40992	3.38423	3.47835	3.46013	3.42236	3.43509	3.43694	3.45813	3.52461	3.467	3.47303	3.45158	3.51038	3.51673	3.48168	3.6036	3.55179	3.60384	3.63859	3.64171	3.62905	3.59909	3.65267	3.66161	3.68359	3.66497	3.60329	3.6336	3.67926	3.75278	3.73815	3.67443	3.63795	3.70231	3.66533	3.91931	3.90857	3.84471	3.91353	4.6746	4.86531	4.03555	4.11412	4.23561	4.52117
adp_gmbh	0.130437	0.135187	0.137281	0.17441	0.173903	0.175788	0.21638	0.214145	0.220453	0.365683	0.365067	0.373757	0.406619	0.412485	0.411453	0.457381	0.456813	0.45488	0.50008	0.496546	0.499269	0.641428	1.14848	0.662961	0.689026	0.686496	0.695506	0.748698	0.763109	0.76246	0.815947	0.818407	0.855545	0.934021	0.927926	0.930044	0.979016	0.980484	0.999209	1.01913	1.01848	1.02604	1.06619	1.08779	1.08015	1.12066	1.12764	1.1288	1.16876	1.18024	1.18304	1.29828	1.31578	1.31994	1.35122	1.36078	1.33491	1.38396	1.39062	1.40174	1.41572	1.42718	1.41426	1.45367	1.50212	1.54737	1.629	1.77318	2.00104	2.24998	2.61392	3.06162	4.33367	4.09796	4.63514
LihO	0.133146	0.134612	0.134648	0.175697	0.17559	0.177427	0.221732	0.218342	0.218391	0.363233	0.367998	0.368506	0.408241	0.413161	0.414054	0.459176	0.46196	0.461679	0.498592	0.510358	0.509126	0.644733	0.642065	0.657747	1.22756	0.699584	0.711025	0.751841	0.755062	0.744157	0.779174	0.780199	0.789521	0.931038	0.935849	0.954129	0.971751	0.985449	0.977745	1.02547	1.01812	1.03311	1.07858	1.07667	1.08211	1.12147	1.12364	1.14075	1.20553	1.20938	1.1946	1.35137	1.32321	1.33653	1.37552	1.38213	1.37107	1.41299	1.42315	1.42967	1.44854	1.44465	1.44855	1.49374	1.53058	1.60591	1.66493	1.82631	2.05441	2.25062	2.67075	3.0798	3.68867	4.11499	5.16166
libcurl	0.368562	0.407932	0.41024	0.629071	0.670976	0.691319	0.918447	0.970725	1.04745	1.29046	1.32689	1.32741	1.56252	1.59809	1.58047	1.85001	1.90847	1.9074	2.1244	2.16088	2.17034	2.38009	2.46765	2.41938	2.64951	2.67721	2.74077	2.95287	3.00535	2.9116	3.16268	3.23702	3.2639	3.49119	3.49484	3.48308	3.72967	3.778	3.81998	4.00746	4.01599	3.98849	4.28185	4.32725	4.32092	4.50267	4.50637	4.56546	4.76766	4.84884	4.81771	5.07249	5.19306	5.34733	5.58479	5.55261	5.56343	5.64327	5.73289	5.79758	6.01446	5.9852	5.90508	6.15877	6.46839	6.83665	7.17291	7.40733	8.77968	10.6584	12.1079	14.8433	17.3067	20.2894	23.7787
user152949	1.52473	1.65298	1.77071	2.09167	2.20589	2.31829	2.64258	2.79838	2.87225	3.25731	3.36725	3.42001	3.83451	3.9549	3.98297	4.34355	4.61771	4.57992	4.91846	5.03753	5.0846	5.39456	5.51518	5.58097	6.12632	6.2005	6.16061	6.51387	6.583	6.92524	7.18224	7.13784	7.25205	7.64068	7.7531	8.00448	8.2758	8.24643	8.33703	8.65576	8.95353	8.98763	9.18868	9.30769	9.39443	9.87169	10.0484	9.89359	10.3836	10.4954	10.5992	10.9085	10.9686	11.0851	11.4787	11.5798	11.6694	11.9691	12.1149	12.1931	12.4919	12.6382	12.7424	13.0695	13.7321	14.2568	15.288	15.8615	18.6555	21.8244	24.4458	30.2765	36.0768	41.6817	47.6459

libcurl and user152949 stands out, being slower by a factor of 5x or more than the others. Here's the same graph without them:

libb64 seems to have a high fixed cost and a low variable cost - it may be that it will outperform other solutions with larger strings. However, here are results going up to 32K:

Implementation	32768
apache	28.9077
jounimalinen	30.4965
NibbleAndAHalf	46.0619
internetsoftwareconsortium	55.3013
polfosol	57.6273
wikibooks_org_c	61.5319
gnome	70.1095
elegantdice	146.471
daedalusalpha	147.503
arduino	148.96
libb64	152.933
manuelmartinez	158.616
CppCodec	199.157
wikibooks_org_cpp	444.807
adp_gmbh	461.506
LihO	477.591
libcurl	2927.97
user152949	5828.38

At 32K, it does not outperform the average performing solutions.

Results for Decoding (32bit Visual Studio 2015)

The results for decoding were a bit surprising:

Implementation	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50	51	52	53	54	55	56	57	58	59	60	61	62	63	64	68	72	76	80	96	112	128	160	192	224	256
polfosol_mod	0.118149	0.123965	0.132323	0.138938	0.145724	0.15001	0.148516	0.150063	0.155588	0.159768	0.1595	0.164923	0.173717	0.171869	0.170223	0.215338	0.215379	0.217386	0.227345	0.22246	0.220268	0.22446	0.225513	0.225432	0.229524	0.231721	0.232686	0.233819	0.233246	0.234697	0.235454	0.23709	0.236167	0.239142	0.23941	0.241255	0.243802	0.243888	0.246725	0.248415	0.25319	0.247676	0.24802	0.252393	0.252219	0.251943	0.255852	0.255103	0.260892	0.257177	0.259487	0.26194	0.264223	0.264778	0.265637	0.264138	0.268398	0.270865	0.268431	0.270159	0.271933	0.27514	0.279219	0.278549	0.283793	0.289054	0.295299	0.301789	0.339051	0.350634	0.377717	0.433025	0.468798	0.518242	0.576378
polfosol	0.100702	0.106826	0.10985	0.109027	0.115617	0.113107	0.115669	0.120866	0.114734	0.120469	0.125517	0.118806	0.123652	0.127979	0.123659	0.214104	0.221051	0.216978	0.217385	0.227613	0.218604	0.224076	0.231008	0.225664	0.228497	0.23411	0.232897	0.233949	0.242163	0.234465	0.240245	0.336396	0.236565	0.236179	0.24456	0.238813	0.243833	0.249231	0.243725	0.244191	0.25537	0.248151	0.250483	0.257389	0.251964	0.255336	0.262606	0.256165	0.2634	0.270868	0.260053	0.264833	0.27039	0.268142	0.270558	0.278209	0.271372	0.278462	0.284137	0.281126	0.275952	0.284681	0.279209	0.284619	0.295511	0.291704	0.315345	0.424631	0.348183	0.36591	0.503937	0.443499	0.494216	0.670382	0.593132
apache	0.110918	0.112637	0.1128	0.115436	0.116796	0.117256	0.120226	0.12004	0.121697	0.125924	0.12684	0.129277	0.133936	0.132658	0.138596	0.21958	0.220991	0.224243	0.228728	0.228149	0.232543	0.238972	0.238143	0.238531	0.243478	0.24403	0.248118	0.251792	0.250145	0.252044	0.257865	0.257694	0.26071	0.270123	0.28246	0.280892	0.289329	0.290967	0.293419	0.296373	0.296761	0.304971	0.29982	0.300682	0.305204	0.30808	0.307939	0.311135	0.318607	0.317292	0.318287	0.325781	0.329487	0.324987	0.332062	0.338251	0.332016	0.331896	0.337249	0.335322	0.342252	0.342699	0.346303	0.350187	0.360007	0.367723	0.383254	0.38926	0.425255	0.462645	0.507067	0.570146	0.633098	0.710881	0.777222
wikibooks_org_c	0.111229	0.113674	0.113631	0.118465	0.122923	0.12456	0.127018	0.130975	0.132442	0.135685	0.138639	0.138558	0.1472	0.149395	0.150609	0.244011	0.244376	0.249126	0.253815	0.255917	0.256338	0.265897	0.267103	0.26592	0.272919	0.277666	0.274635	0.281842	0.286899	0.289247	0.288052	0.294788	0.295424	0.300546	0.302239	0.30244	0.307853	0.313565	0.319349	0.319623	0.321207	0.324357	0.343912	0.34685	0.342734	0.352803	0.348426	0.35024	0.356155	0.357952	0.360195	0.365395	0.373828	0.371551	0.37223	0.375427	0.377431	0.383825	0.389348	0.385482	0.392131	0.392381	0.394248	0.407817	0.418862	0.428187	0.44587	0.442508	0.491097	0.533593	0.584836	0.664605	0.750631	0.843889	0.929109
gnome	0.135306	0.136542	0.135691	0.149475	0.152061	0.152209	0.158331	0.160255	0.162773	0.17057	0.168067	0.169957	0.253128	0.253458	0.251367	0.26852	0.269152	0.269162	0.275943	0.274272	0.276532	0.291552	0.289895	0.288	0.306479	0.305429	0.308619	0.322579	0.324028	0.324958	0.326201	0.324285	0.326481	0.337239	0.335942	0.337768	0.346142	0.347202	0.344783	0.355155	0.357403	0.357442	0.370493	0.373733	0.378674	0.380645	0.380386	0.382733	0.390098	0.390588	0.391698	0.401697	0.400481	0.404134	0.411172	0.410863	0.414036	0.424345	0.420461	0.427035	0.435667	0.437693	0.437641	0.447751	0.465231	0.46402	0.489124	0.48997	0.544025	0.606479	0.65449	0.746712	0.857911	0.963168	1.07402
wikibooks_org_cpp	0.137107	0.143881	0.144249	0.157493	0.167668	0.166939	0.272989	0.275596	0.277678	0.286578	0.294554	0.292632	0.306579	0.311492	0.288697	0.368052	0.376547	0.380167	0.391983	0.395297	0.38637	0.403056	0.400953	0.387332	0.451675	0.413564	0.405364	0.43265	0.426948	0.446417	0.442825	0.442383	0.438331	0.452489	0.467213	0.45386	0.461765	0.470416	0.469397	0.478324	0.486763	0.483466	0.489407	0.491247	0.491441	0.502955	0.517575	0.510192	0.520073	0.5276	0.524447	0.531122	0.539423	0.532325	0.554438	0.557554	0.557664	0.567017	0.573378	0.559811	0.579846	0.580522	0.579341	0.583715	0.620598	0.623914	0.659549	0.671767	0.767635	0.823613	0.935837	1.0578	1.20203	1.38228	1.48052
elegantdice	0.110253	0.110717	0.114073	0.126882	0.127934	0.132785	0.143723	0.145128	0.148095	0.161278	0.166388	0.165971	0.170482	0.173628	0.174986	0.2808	0.284577	0.28003	0.296702	0.304132	0.305162	0.322427	0.324715	0.327566	0.342098	0.34322	0.347111	0.354373	0.354776	0.359475	0.362939	0.37055	0.373218	0.381399	0.384892	0.393644	0.400445	0.404646	0.407535	0.416576	0.419383	0.419186	0.430232	0.433547	0.439159	0.447181	0.449758	0.454912	0.476521	0.465976	0.468736	0.480808	0.480806	0.484784	0.49477	0.501236	0.499485	0.507143	0.519608	0.524873	0.534632	0.533557	0.542253	0.538959	0.56585	0.580285	0.606438	0.631546	0.73393	0.818926	0.903711	1.09694	1.29304	1.44603	1.65048
arduino	0.124367	0.129139	0.122853	0.144411	0.144237	0.140172	0.158969	0.158972	0.155904	0.179376	0.178192	0.171242	0.193384	0.192319	0.186305	0.294035	0.294898	0.285843	0.307517	0.309945	0.296224	0.32307	0.327402	0.324803	0.333095	0.341734	0.338541	0.357104	0.361581	0.364713	0.374631	0.375415	0.363743	0.385654	0.387632	0.386409	0.406941	0.403615	0.405239	0.422092	0.422958	0.417488	0.435613	0.445673	0.436503	0.460092	0.457328	0.454343	0.470617	0.468529	0.467974	0.483275	0.494465	0.488319	0.511491	0.508885	0.505187	0.523265	0.522181	0.519024	0.537168	0.544286	0.53834	0.554658	0.580675	0.594415	0.633319	0.642401	0.743742	0.835796	0.92895	1.11668	1.28449	1.46472	1.67344
daedalusalpha	0.118872	0.121192	0.121848	0.135331	0.13691	0.139903	0.153741	0.151942	0.161192	0.261438	0.26775	0.265254	0.268295	0.269995	0.274087	0.396683	0.388986	0.386266	0.399761	0.401692	0.404879	0.416053	0.419976	0.417408	0.431806	0.442834	0.433005	0.454489	0.458858	0.460195	0.475104	0.473412	0.476723	0.491433	0.494367	0.490745	0.509819	0.505507	0.513231	0.527995	0.53051	0.528185	0.542537	0.55311	0.550359	0.553384	0.55582	0.557484	0.57459	0.575148	0.577239	0.59679	0.594004	0.58973	0.60626	0.619204	0.61469	0.632568	0.632142	0.632482	0.64574	0.647673	0.650678	0.661728	0.684214	0.689957	0.729101	0.745124	0.864841	0.951392	1.03651	1.23389	1.41346	1.58532	1.80518
jounimalinen	0.138513	0.142186	0.139679	0.158851	0.162742	0.162503	0.179105	0.183804	0.185565	0.202405	0.20255	0.201732	0.228746	0.231243	0.22742	0.320218	0.319816	0.319282	0.347276	0.341953	0.343176	0.365368	0.362035	0.36467	0.388292	0.390051	0.384603	0.402121	0.400377	0.398604	0.4214	0.42246	0.423776	0.445186	0.441227	0.445614	0.462731	0.465229	0.472534	0.488886	0.491193	0.487079	0.513324	0.513113	0.513193	0.53251	0.531242	0.533583	0.564113	0.562036	0.557499	0.580192	0.579357	0.579187	0.600007	0.601091	0.597094	0.619757	0.626183	0.615954	0.640525	0.641702	0.643635	0.664388	0.685832	0.727263	0.744369	0.772203	0.877957	1.0066	1.14153	1.32958	1.56197	1.78555	2.01
manuelmartinez	0.4096	0.415059	0.418558	0.419317	0.42672	0.429873	0.435647	0.438081	0.438351	0.447444	0.452479	0.456624	0.472904	0.463203	0.467611	0.572164	0.578248	0.572058	0.583636	0.586632	0.589347	0.596787	0.599801	0.599387	0.605057	0.613691	0.615267	0.622288	0.624223	0.628015	0.635372	0.752441	0.73623	0.779458	0.749197	0.76287	0.758522	0.760997	0.761078	0.772036	0.776618	0.77998	0.785183	0.791034	0.79432	0.801088	0.806067	0.907364	0.913254	0.911815	0.917691	0.930092	0.923876	0.927857	0.937557	0.942161	0.944444	0.94667	0.950312	0.957629	0.96135	0.966275	0.967384	0.98425	0.990668	1.11189	1.1212	1.14196	1.23319	1.42418	1.51098	1.79945	1.93607	2.10536	2.42382
CppCodec	0.141055	0.146972	0.140593	0.181367	0.182313	0.181108	0.212921	0.214477	0.214351	0.252656	0.253499	0.249121	0.280565	0.286318	0.284566	0.413248	0.416572	0.414782	0.451	0.451216	0.456696	0.492785	0.50021	0.485557	0.519536	0.518877	0.526112	0.56784	0.560439	0.580831	0.604624	0.604575	0.611048	0.637289	0.657838	0.647043	0.687636	0.680906	0.687179	0.710969	0.737747	0.725958	0.755492	0.755487	0.754503	0.792972	0.804889	0.82052	0.834846	0.838023	0.849878	0.867839	0.873208	0.880266	0.907843	0.921311	0.930049	0.955656	0.951569	0.958065	0.990717	0.985925	1.00017	1.02112	1.09015	1.11958	1.19885	1.24361	1.47434	1.66321	1.87575	2.34964	2.777	3.28984	3.7337
libb64	2.45013	2.38854	2.38942	2.37937	2.38886	2.39571	2.43787	2.43099	2.44393	2.42543	2.4129	2.42727	2.4569	2.44502	2.41129	2.48738	2.50328	2.51153	2.52321	2.55586	2.51755	2.56064	2.53932	2.53629	2.55393	2.59423	2.57251	2.59712	2.59477	2.5966	2.6001	2.60077	2.7165	2.73357	2.72781	2.75023	2.76679	2.75997	2.76055	2.77294	2.77958	2.7895	2.77479	2.78064	2.77567	2.78998	2.78712	2.79883	2.83423	2.82572	2.84713	2.80915	2.80519	2.80176	2.86118	2.83038	2.82786	2.86934	2.86758	2.87922	2.88215	2.8665	2.85726	2.87552	3.00114	3.04033	3.02809	3.05946	3.13153	3.34955	3.43876	3.62757	3.73788	3.81225	3.96402
internetsoftwareconsortium	0.135604	0.161758	0.164959	0.213854	0.221899	0.237674	0.238722	0.278391	0.279141	0.328501	0.357319	0.378045	0.485605	0.492634	0.519268	0.551103	0.591382	0.591928	0.625235	0.669193	0.642841	0.698284	0.67928	0.716567	0.700509	0.751279	0.760212	0.820691	0.812954	0.851921	0.874513	0.854343	0.891177	0.920454	0.970358	0.959435	1.00258	1.01985	1.08718	1.08046	1.02682	1.13023	1.11809	1.16744	1.13436	1.19687	1.18659	1.2619	1.28069	1.26708	1.25916	1.24536	1.30387	1.35724	1.39534	1.36466	1.42567	1.5076	1.42347	1.42681	1.44594	1.49135	1.5436	1.54534	1.65416	1.67699	1.83365	1.9143	2.20027	2.61396	2.93622	3.61259	4.28036	5.08986	5.88355
libcurl	0.135269	0.221731	0.189595	0.278441	0.324443	0.413472	0.294828	0.353842	0.453577	0.409958	0.514761	0.586416	0.540828	0.654843	0.625509	0.840788	0.866102	0.94519	1.03432	1.07686	0.874499	1.02816	1.06249	1.02864	0.930506	1.04686	1.21774	1.40605	1.09711	1.52958	1.48269	1.23179	1.38481	1.54769	1.60625	1.5103	1.68827	1.61818	1.70365	1.70151	1.59113	1.90182	1.87365	1.87054	1.99713	2.00215	1.92933	2.31003	2.22478	2.10063	2.26262	2.13731	2.12481	2.16748	2.53915	2.36186	2.57919	2.48771	2.35429	2.18735	2.50237	2.67865	2.92517	2.63335	3.03366	2.9372	3.29791	3.46938	4.2146	4.65982	5.28627	6.82438	8.04001	9.33265	11.3955
LihO	0.200832	0.219694	0.199774	0.345344	0.34456	0.357022	0.420983	0.438748	0.453982	0.555253	0.576945	0.601498	0.677472	0.711815	0.694353	0.932264	0.941825	0.939055	1.07929	1.09149	1.01839	1.19763	1.18776	1.16446	1.22621	1.27843	1.30797	1.46068	1.36537	1.48128	1.55953	1.55582	1.62049	1.76178	1.75628	1.73165	1.89915	1.85592	1.9164	2.46059	1.9596	2.02557	2.10593	2.11938	2.16339	2.27857	2.21685	2.45059	2.53162	2.46273	2.52609	2.53832	2.54423	2.57708	2.77029	2.72944	2.81704	2.84926	2.79135	2.73187	2.92682	3.02826	3.03176	3.09953	3.30152	3.42744	3.77803	3.88581	4.56597	5.21808	5.91771	7.68035	8.66661	10.4439	12.6315
adp_gmbh	0.209475	0.234301	0.214723	0.36542	0.374458	0.391939	0.466609	0.489803	0.510785	0.610815	0.66594	0.682442	0.771804	0.817743	0.810188	1.05309	1.0621	1.10696	1.23201	1.24374	1.17008	1.35006	1.35821	1.33779	1.36942	1.47349	1.50232	1.67442	1.5531	1.67777	1.82921	1.79899	1.87766	2.00309	2.04931	1.9613	2.17817	2.13072	2.18533	2.26772	2.24121	2.35696	2.47487	2.43142	2.48025	2.59841	2.56752	2.76805	2.91337	2.8522	2.86643	2.96925	2.93879	2.95373	3.12177	3.0836	3.199	3.2406	3.18348	3.23138	3.39761	3.42359	3.52741	4.16719	3.84944	4.0173	4.32387	4.42701	5.2434	6.18663	6.90654	8.9877	10.3403	12.1351	14.3773
user152949	1.56263	1.72881	1.83673	2.16248	2.33526	2.43341	2.7817	2.92215	3.06089	3.36212	3.52552	3.61884	3.94919	4.16032	4.22839	4.68393	4.82273	4.94147	5.26418	5.49898	5.52942	5.82988	6.02082	6.12667	6.43054	6.64832	6.74578	7.08192	7.19858	7.3667	7.66561	7.79815	7.99703	8.28286	8.48972	8.62092	8.91568	9.11106	9.16898	9.50423	9.6593	9.83468	10.1351	10.3154	10.438	10.8461	10.969	10.9927	11.2078	11.4015	11.5855	11.9239	12.2725	12.1929	12.5762	12.7439	12.8227	13.2369	13.4012	13.3287	13.7715	13.9274	13.9946	14.3755	15.1852	15.867	16.7722	17.5232	20.6807	24.1109	27.3195	33.9019	40.1385	46.9977	53.1124

Removing the slowest implementations:

The fastest implementation is polfosol's snippet from Stack Overflow. What's even more surprising is that by looking just a few minutes at the code, I was able to juice it a little bit more - The implementation is allocating a std::string and then setting the characters using the operator[]. It turns out that operator[] on std::string has some checks for out of bound. Since it is impossible to be out of bound in this context, I changed the code to use the operator[] on a unchecked char pointer and was able to get another 10-15% boost.

Here are the results for a 32K buffer:

Implementation	32768
polfosol_mod	46.5851
polfosol	52.1657
apache	72.8494
wikibooks_org_c	88.3819
gnome	107.384
libb64	120.313
manuelmartinez	159.883
elegantdice	181.565
daedalusalpha	186.847
jounimalinen	230.102
arduino	381.613
wikibooks_org_cpp	405.629
CppCodec	652.674
internetsoftwareconsortium	1029.55
libcurl	1461.21
LihO	2199.47
adp_gmbh	2304.03
user152949	6510.23

Conclusion

• For encoding. the Apache and the Internet Software Consortium versions, written over 15 years ago, beats most of the code snippets posted around - which brings us back to how it is important to look for existing implementations before writing new ones. The ISC implementation comes with an unconvenient license from IBM, however, granting you "immunity from suites under its patents, if any, for the use, sale or manufacture of produces to the extent that such products are used for performing Domain Name System";
• Some other implementations are terrible, the slower ones generally allocate memory dynamically as they convert, even though the output size is deterministic and can be preallocated;
• libb64 shows very strange performance results - I get the feeling that they are doing something neat but that I am perhaps not using their code right;
• A lot of implementations are available, everyone claims theirs is better. This test shows that unless you measure, you cannot make any claims about the performance of your code;

If you do not need support for line breaks and don't need validation of data integrity, I would recommend using Jouni Malinen or the Apache's implementation for the Encoder, and the modified Polfosol implementation for decoding.

Keep in mind that these results were all obtained using Visual Studio and could differ on another compiler.