commit 68108a4aa05489ffac8c941ae90c4d995f4eaa47
from: Sven M. Hallberg <pesco@khjk.org>
date: Wed Jun 14 13:16:21 2023 UTC

statically allocate global lzw decoder context

Avoids the use of malloc(). Also factors out table initialization to a
function lzw_init_table().

commit - 1afde767c483e9672beed15c549717de2db061da
commit + 68108a4aa05489ffac8c941ae90c4d995f4eaa47
blob - 7bb22711853d9cc43175aa795e1b504f6811abcb
blob + b079e588e6363b61fd3b5cfe6c64418fb6649429
--- lzw.c
+++ lzw.c
@@ -1,6 +1,5 @@
 #include <hammer/hammer.h>
 #include <hammer/glue.h>
-#include <stdlib.h>	/* malloc, free */
 #include <string.h>	/* memcpy */
 #include "lzw.h"
 
@@ -50,6 +49,20 @@ struct context {
  */
 
 static void
+lzw_init_table(struct context *ctx)
+{
+	int i;
+
+	/* set up the static entries */
+	for(i = 0; i < 256; i++) {
+		ctx->table[i].len = 1;
+		ctx->table[i].prefix = -1;	/* none */
+		ctx->table[i].first = i;
+		ctx->table[i].last = i;
+	}
+}
+
+static void
 lzw_clear_table(struct context *ctx)
 {
 	ctx->next = 258;
@@ -96,7 +109,7 @@ lzw_code_string(struct context *ctx, int code, uint8_t
  */
 
 HParser *p_lzwdata;
-static struct context *context;
+static struct context context;
 
 
 /*
@@ -262,18 +275,8 @@ kcodeword(HAllocator *mm__, const HParsedToken *x, voi
 void
 init_LZW_parser()
 {
-	int i;
-
 	/* initialize global context variable, incl. static table entries */
-	context = malloc(sizeof *context);
-	assert(context != NULL);
-	for(i = 0; i < 256; i++)
-	{
-		context->table[i].len = 1;
-		context->table[i].prefix = -1;	/* none */
-		context->table[i].first = i;
-		context->table[i].last = i;
-	}
+	lzw_init_table(&context);
 	init_LZW_context(1);
 
 	/* static parsers for code words of all possible sizes */
@@ -283,13 +286,13 @@ init_LZW_parser()
 	p_code12 = h_bits(12, false);
 
 	/* kcodeword() selects the appropriate parser based on context */
-	H_RULE   (codeword,	h_bind(h_epsilon_p(), kcodeword, context));
+	H_RULE   (codeword,	h_bind(h_epsilon_p(), kcodeword, &context));
 
 	H_VRULE  (eod,		codeword);
-	H_AVDRULE(clear,	codeword, context);
-	H_AVDRULE(output,	codeword, context);
+	H_AVDRULE(clear,	codeword, &context);
+	H_AVDRULE(output,	codeword, &context);
 
-	H_ADRULE(lzwblock,	h_right(clear, h_many(output)), context);
+	H_ADRULE(lzwblock,	h_right(clear, h_many(output)), &context);
 	H_ARULE (lzwdata,	h_left(h_many1(lzwblock), eod));
 	    // XXX validate that the last byte is zero-padded?
 	    // XXX require h_end_p()?
@@ -307,6 +310,6 @@ parse_LZW_data(const uint8_t *input, size_t length)
 void
 init_LZW_context(int earlychange)
 {
-	lzw_clear_table(context);
-	context->earlychange = !!earlychange;
+	lzw_clear_table(&context);
+	context.earlychange = !!earlychange;
 }