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1 files changed, 103 insertions, 0 deletions

diff --git a/src/varint.c b/src/varint.c
new file mode 100644
index 0000000..da7e480
--- /dev/null
+++ b/src/varint.c
@@ -0,0 +1,103 @@
+#include <stdint.h>
+
+void
+encode_varint(uint8_t *data, uint32_t *write, int64_t value, uint32_t left)
+{
+	uint32_t pos = 0;
+
+	if (value < 0) {
+		*write = 0;
+		return;
+	}
+
+	if (value < 0x80) {
+		data[pos++] = value & 0xFF;
+	} else if (value < 0x4000) {
+		data[pos++] = 0x80 | ((value & 0xFF00 ) >> 8);
+		data[pos++] = value & 0xFF;
+	} else if (value < 0x200000) {
+		data[pos++] = 0xC0 | ((value & 0xFF0000) >> 16);
+		data[pos++] = ((value & 0xFF00) >> 8) & 0xFF;
+		data[pos++] = value & 0xFF;
+	} else if (value < 0x10000000) {
+		data[pos++] = 0xE0 | ((value ) >> 24);
+		data[pos++] = (value >> 16) & 0xFF;
+		data[pos++] = (value >> 8) & 0xFF;
+		data[pos++] = value & 0xFF;
+	} else if (value < 0x100000000LL) {
+		data[pos++] = 0xF0;
+		data[pos++] = (value >> 24) & 0xFF;
+		data[pos++] = (value >> 16) & 0xFF;
+		data[pos++] = (value >> 8) & 0xFF;
+		data[pos++] = value & 0xFF;
+	} else {
+		data[pos++] = 0xF4;
+		data[pos++] = (value >> 56) & 0xFF;
+		data[pos++] = (value >> 48) & 0xFF;
+		data[pos++] = (value >> 40) & 0xFF;
+		data[pos++] = (value >> 32) & 0xFF;
+		data[pos++] = (value >> 24) & 0xFF;
+		data[pos++] = (value >> 16) & 0xFF;
+		data[pos++] = (value >> 8) & 0xFF;
+		data[pos++] = value & 0xFF;
+	}
+
+	*write = pos;
+}
+
+int64_t
+decode_varint(uint8_t *data, uint32_t *read, uint32_t left)
+{
+	int64_t varint = 0;
+
+	/* 1 byte with 7 · 8 + 1 leading zeroes */
+	if ((data[0] & 0x80) == 0x00) {
+		varint = data[0] & 0x7F;
+		*read = 1;
+	/* 2 bytes with 6 · 8 + 2 leading zeroes */
+	} else if ((data[0] & 0xC0) == 0x80) {
+		varint = ((data[0] & 0x3F) << 8) | data[1];
+		*read = 2;
+	/* 3 bytes with 5 · 8 + 3 leading zeroes */
+	} else if ((data[0] & 0xE0) == 0xC0) {
+		varint = (((data[0] & 0x1F) << 16) |
+			    (data[1] << 8) | (data[2]));
+		*read = 3;
+	/* 4 bytes with 4 · 8 + 4 leading zeroes */
+	} else if ((data[0] & 0xF0) == 0xE0) {
+		varint = (((data[0] & 0x0F) << 24) | (data[1] << 16) |
+			  (data[2] << 8) | (data[3]));
+		*read = 4;
+	} else /* if ((data[pos] & 0xF0) == 0xF0) */ {
+		switch (data[0] & 0xFC) {
+		/* 32-bit positive number */
+		case 0xF0:
+			varint = ((data[1] << 24) | (data[2] << 16) |
+				  (data[3] << 8) | data[4]);
+			*read = 1 + 4;
+			break;
+		/* 64-bit number */
+		case 0xF4:
+			varint =
+				((int64_t)data[1] << 56) | ((int64_t)data[2] << 48) |
+				((int64_t)data[3] << 40) | ((int64_t)data[4] << 32) |
+				(data[5] << 24) | (data[6] << 16) |
+				(data[7] <<  8) | (data[8] <<  0);
+			*read = 1 + 8;
+			break;
+		/* Negative varint */
+		case 0xF8:
+			/* FIXME: handle endless recursion */
+			varint = -decode_varint(&data[1], read, left - 1);
+			*read += 1;
+			break;
+		/* Negative two bit number */
+		case 0xFC:
+			varint = -(int)(data[0] & 0x03);
+			*read = 1;
+			break;
+		}
+	}
+
+	return varint;
+}