cbase64.h

/* cbase64 - public domain base64 encoder/decoder

    Do this:
        #define CBASE64_IMPLEMENTATION
    before you include this file in *one* C or C++ file to create the implementation.

    // i.e. it should look like this:
   #include ...
   #include ...
   #include ...
   #define CBASE64_IMPLEMENTATION
   #include "cbase64.h"

*/

#ifndef CBASE64_H
#define CBASE64_H

#ifdef __cplusplus
extern "C" {
#endif

typedef enum { step_A, step_B, step_C, step_D } cbase64_step;

typedef struct {
	cbase64_step step;
	unsigned char result;
} cbase64_encodestate;

typedef struct {
	cbase64_step step;
	char result;
} cbase64_decodestate;

void cbase64_init_encodestate(cbase64_encodestate *state_in);
void cbase64_init_decodestate(cbase64_decodestate *state_in);

unsigned int cbase64_calc_encoded_length(unsigned int length_in);
unsigned int cbase64_calc_decoded_length(const char *code_in, unsigned int length_in);

unsigned int cbase64_encode_block(const unsigned char *data_in, unsigned int length_in, char *code_out, cbase64_encodestate *state_in);

unsigned int cbase64_decode_block(const char *code_in, unsigned int length_in, unsigned char *data_out, cbase64_decodestate *state_in);

unsigned int cbase64_encode_blockend(char *code_out, cbase64_encodestate *state_in);

#ifdef __cplusplus
}
#endif

#endif // CBASE64_H

#ifdef CBASE64_IMPLEMENTATION

char cbase64__encode_value(unsigned char value_in)
{
	static const char *encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	return encoding[(int)value_in];
}

char cbase64__decode_value(char value_in)
{
	static const char decoding[] = {62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0,  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, -1, -1, -1, -1, -1, -1,
					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};
	static const char decoding_size = sizeof(decoding);
	value_in -= 43;
	if (value_in < 0 || value_in >= decoding_size)
		return -1;
	return decoding[(int)value_in];
}

void cbase64_init_encodestate(cbase64_encodestate *state_in)
{
	state_in->step = step_A;
	state_in->result = '\0';
}

void cbase64_init_decodestate(cbase64_decodestate *state_in)
{
	state_in->step = step_A;
	state_in->result = '\0';
}

unsigned int cbase64_calc_encoded_length(unsigned int length_in)
{
	return 4 * (length_in / 3) + ((length_in % 3 != 0) ? 4 : 0);
}

unsigned int cbase64_calc_decoded_length(const char *code_in, unsigned int length_in)
{
	if (length_in == 0 || ((length_in & 3) != 0)) {
		return 0;
	}
	const char secondlast = code_in[length_in - 2];
	const char last = code_in[length_in - 1];
	return 3 * (length_in / 4) - (secondlast == '=') - (last == '=');
}

unsigned int cbase64_encode_block(const unsigned char *data_in, unsigned int length_in, char *code_out, cbase64_encodestate *state_in)
{
	const unsigned char *datachar = data_in;
	const unsigned char *const datatextend = data_in + length_in;
	char *codechar = code_out;
	unsigned char result = state_in->result;
	unsigned char fragment;

	switch (state_in->step) {
		for (;;) {
		case step_A:
			if (datachar == datatextend) {
				state_in->step = step_A;
				state_in->result = result;
				return uint32_t(codechar - code_out);
			}
			fragment = *datachar++;
			result = (fragment & 0x0fc) >> 2;
			*codechar++ = cbase64__encode_value(result);
			result = (fragment & 0x003) << 4;
		case step_B:
			if (datachar == datatextend) {
				state_in->step = step_B;
				state_in->result = result;
				return uint32_t(codechar - code_out);
			}
			fragment = *datachar++;
			result |= (fragment & 0x0f0) >> 4;
			*codechar++ = cbase64__encode_value(result);
			result = (fragment & 0x00f) << 2;
		case step_C:
			if (datachar == datatextend) {
				state_in->step = step_C;
				state_in->result = result;
				return uint32_t(codechar - code_out);
			}
			fragment = *datachar++;
			result |= (fragment & 0x0c0) >> 6;
			*codechar++ = cbase64__encode_value(result);
			result = (fragment & 0x03f) >> 0;
			*codechar++ = cbase64__encode_value(result);
		}
	}
	// control should not reach here
	return uint32_t(codechar - code_out);
}

unsigned int cbase64_decode_block(const char *code_in, unsigned int length_in, unsigned char *data_out, cbase64_decodestate *state_in)
{
	const char *codechar = code_in;
	const char *const codeend = code_in + length_in;
	unsigned char *datachar = data_out;
	char fragment;
	char overwrite = state_in->result;

	switch (state_in->step) {
		for (;;) {
		case step_A:
			do {
				if (codechar == codeend) {
					state_in->step = step_A;
					state_in->result = overwrite;
					return uint32_t(datachar - data_out);
				}
				fragment = cbase64__decode_value(*codechar++);
			} while (fragment < 0);
			*datachar = (fragment & 0x03f) << 2;
		case step_B:
			do {
				if (codechar == codeend) {
					state_in->step = step_B;
					state_in->result = overwrite;
					return uint32_t(datachar - data_out);
				}
				fragment = cbase64__decode_value(*codechar++);
			} while (fragment < 0);
			*datachar++ |= (fragment & 0x030) >> 4;
			overwrite = (fragment & 0x00f) << 4;
		case step_C:
			do {
				if (codechar == codeend) {
					state_in->step = step_C;
					state_in->result = overwrite;
					return uint32_t(datachar - data_out);
				}
				fragment = cbase64__decode_value(*codechar++);
			} while (fragment < 0);
			*datachar++ = overwrite | (fragment & 0x03c) >> 2;
			overwrite = (fragment & 0x003) << 6;
		case step_D:
			do {
				if (codechar == codeend) {
					state_in->step = step_D;
					state_in->result = overwrite;
					return uint32_t(datachar - data_out);
				}
				fragment = cbase64__decode_value(*codechar++);
			} while (fragment < 0);
			*datachar++ = overwrite | (fragment & 0x03f);
		}
	}
	// control should not reach here
	return uint32_t(datachar - data_out);
}

unsigned int cbase64_encode_blockend(char *code_out, cbase64_encodestate *state_in)
{
	char *codechar = code_out;
	switch (state_in->step) {
	case step_B:
		*codechar++ = cbase64__encode_value(state_in->result);
		*codechar++ = '=';
		*codechar++ = '=';
		break;
	case step_C:
		*codechar++ = cbase64__encode_value(state_in->result);
		*codechar++ = '=';
		break;
	case step_A:
		break;
	}
	return uint32_t(codechar - code_out);
}

#endif // CBASE64_IMPLEMENTATION