X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;ds=sidebyside;f=dehuff.c;fp=dehuff.c;h=3e0fd6c4ec86ab441ca36c921cb134d1cf842228;hb=47de6c270a336574dce220cde780a802a513d113;hp=0000000000000000000000000000000000000000;hpb=71b4fae2b31acf415c3b07a019ae252f4d128952;p=fjl

diff --git a/dehuff.c b/dehuff.c
new file mode 100644
index 0000000..3e0fd6c
--- /dev/null
+++ b/dehuff.c
@@ -0,0 +1,127 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#include "dehuff.h"
+
+void reliable_read(raw_input_func_t* input_func, void* userdata, uint8_t* buf, size_t len)
+{
+	while (len > 0) {
+		ssize_t bytes_read = input_func(userdata, buf, len);
+		assert(bytes_read <= len);
+
+		// TODO: We need better error handling here. setjmp()/longjmp()
+		// should hopefully do the trick, but we need to take care for
+		// suspension.
+		if (bytes_read == (ssize_t)-1) {
+			fprintf(stderr, "Input function returned error\n");
+			exit(1);
+		}
+		if (bytes_read == 0) {
+			fprintf(stderr, "Premature EOF\n");
+			exit(1);
+		}
+
+		buf += bytes_read;
+		len -= bytes_read;
+	}
+}
+
+uint16_t read_length(raw_input_func_t* input_func, void* userdata)
+{
+	uint8_t buf[2];
+	reliable_read(input_func, userdata, buf, 2);
+	return (buf[0] << 8) | buf[1];
+}
+
+void read_huffman_tables(huffman_tables_t* dst, raw_input_func_t* input_func, void* userdata)
+{
+	size_t len = read_length(input_func, userdata);
+	assert(len > 2);
+	len -= 2;
+
+	// TODO: check for NULL return
+	uint8_t* buf = (uint8_t*)malloc(len);
+	uint8_t* inptr = buf;
+	reliable_read(input_func, userdata, buf, len);
+	
+	while (len > 0) {
+		unsigned char tc_th = *inptr++;
+		--len;
+		unsigned table_class = tc_th >> 4;
+		unsigned table_dest = tc_th & 0x0f;
+		
+		if (table_class != 0 && table_class != 1) {
+			fprintf(stderr, "Error: Unknown table class %u\n", table_class);
+			exit(1);
+		}
+		if (table_dest >= 4) {
+			fprintf(stderr, "Error: Unknown table destination %u\n", table_dest);
+			exit(1);
+		}
+
+		struct huffman_table* tbl = dst[table_class][table_dest];
+		if (len < 16) {
+			fprintf(stderr, "Short read for num_codes\n");
+			exit(1);
+		}
+		for (unsigned i = 0; i < 16; ++i) {
+			tbl->num_codes[i] = *inptr++;
+			--len;
+		}
+		for (unsigned i = 0, k = 0; i < 16; ++i) {
+			if (len < tbl->num_codes[i]) {
+				fprintf(stderr, "Short read for codes\n");
+				exit(1);
+			}
+			for (unsigned j = 0; j < tbl->num_codes[i]; ++j, ++k) {
+				tbl->codes[k] = *inptr++;
+				--len;
+			}
+		}
+
+		// Generate derived tables
+
+		// generate_size_table (figure C.1)
+		{
+			unsigned k = 0;
+			for (unsigned i = 0; i < 16; ++i) {
+				for (unsigned j = 0; j < tbl->num_codes[i]; ++j, ++k) {
+					tbl->huffsize[k] = i + 1;
+				}
+			}
+			tbl->huffsize[k] = 0;
+		}
+
+		// generate_code_table (figure C.2)
+		unsigned si = tbl->huffsize[0];
+		for (unsigned i = 0, j = 0;; ) {
+			tbl->huffcode[i++] = j++;
+			if (tbl->huffsize[i] == si) {
+				continue;
+			}
+			if (tbl->huffsize[i] == 0) {
+				break;
+			}
+
+			do {
+				j <<= 1;
+			} while (++si != tbl->huffsize[i]);
+		}
+
+		// decoder_tables (figure F.15)
+		for (unsigned i = 0, j = 0; i < 16; ++i) {
+			if (tbl->num_codes[i] == 0) {
+				tbl->maxcode[i] = -1;
+				continue;
+			}
+
+			tbl->valptr[i] = j;
+			tbl->mincode[i] = tbl->huffcode[j];
+			j += tbl->num_codes[i];
+			tbl->maxcode[i] = tbl->huffcode[j - 1];
+		}
+	}
+
+	free(buf);
+}