From e3aa668ef358739148adb1a4965b629d07467575 Mon Sep 17 00:00:00 2001
From: Leo Tenenbaum <pommicket@gmail.com>
Date: Tue, 24 Nov 2020 17:03:23 -0500
Subject: loading a file

---
 buffer.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 buffer.c

(limited to 'buffer.c')

diff --git a/buffer.c b/buffer.c
new file mode 100644
index 0000000..78fcc1a
--- /dev/null
+++ b/buffer.c
@@ -0,0 +1,116 @@
+// Text buffers - These store the contents of a file.
+// To make inserting characters faster, the file contents are split up into
+// blocks of a few thousand bytes. Block boundaries are not necessarily
+// on character boundaries, so one block might have part of a UTF-8 character
+// with the next block having the rest.
+#include "util.c"
+
+#define TEXT_BLOCK_MAX_SIZE 400
+// Once two adjacent blocks are at most this big, combine them into
+// one bigger text block.
+#define TEXT_BLOCK_COMBINE_SIZE (3*(TEXT_BLOCK_MAX_SIZE / 4))
+// A good size for text blocks to be. When a file is loaded, there
+// shouldn't be just full blocks, because they will all immediately split.
+// Instead, we use blocks of this size.
+#define TEXT_BLOCK_DEFAULT_SIZE (3*(TEXT_BLOCK_MAX_SIZE / 4))
+typedef struct {
+	u16 len;
+	char *contents;
+} TextBlock;
+
+typedef struct {
+	u32 nblocks; // number of text blocks
+	TextBlock *blocks;
+} TextBuffer;
+
+// Returns a new block added at index `where`,
+// or NULL if there's not enough memory.
+static TextBlock *text_buffer_add_block(TextBuffer *buffer, u32 where) {
+	// make sure we can actually allocate enough memory for the contents of the block
+	// before doing anything
+	char *block_contents = calloc(1, TEXT_BLOCK_MAX_SIZE);
+	if (!block_contents) {
+		return NULL;
+	}
+
+	u32 nblocks_before = buffer->nblocks;
+	u32 nblocks_after = buffer->nblocks + 1;
+	if (util_is_power_of_2(nblocks_after)) {
+		// whenever the number of blocks is a power of 2, we need to grow the blocks array.
+		buffer->blocks = realloc(buffer->blocks, 2 * nblocks_after * sizeof *buffer->blocks);
+		if (!buffer->blocks) {
+			// out of memory
+			free(block_contents);
+			return NULL;
+		}
+	}
+	if (where != nblocks_before) { // if we aren't just inserting the block at the end,
+		// make space for the new block
+		memmove(buffer->blocks + (where + 1), buffer->blocks + where, nblocks_before - where);
+	}
+	
+	TextBlock *block = buffer->blocks + where;
+	util_zero_memory(block, sizeof *buffer->blocks); // zero everything
+	block->contents = block_contents;
+
+	
+	buffer->nblocks = nblocks_after;
+	return block;
+}
+
+Status text_buffer_load_file(TextBuffer *buffer, FILE *fp) {
+	char block_contents[TEXT_BLOCK_DEFAULT_SIZE];
+	size_t bytes_read;
+
+	util_zero_memory(buffer, sizeof *buffer);
+	
+	// read file one block at a time
+	do {
+		bytes_read = fread(block_contents, 1, sizeof block_contents, fp);
+		if (bytes_read > 0) {
+			TextBlock *block = text_buffer_add_block(buffer, buffer->nblocks);
+			if (!block) {
+				return false;
+			}
+			memcpy(block->contents, block_contents, bytes_read);
+			block->len = (u16)bytes_read;
+		}
+	} while (bytes_read == sizeof block_contents);
+	if (ferror(fp))	
+		return false;
+	return true;
+}
+
+static void text_buffer_print_internal(TextBuffer *buffer, bool debug) {
+	printf("\033[2J\033[;H");
+	TextBlock *blocks = buffer->blocks;
+	u32 nblocks = buffer->nblocks;
+	
+	for (u32 i = 0; i < nblocks; ++i) {
+		TextBlock *block = &blocks[i];
+		fwrite(block->contents, 1, block->len, stdout);
+		if (debug)
+			printf("\n\n------\n\n"); // NOTE: could be bad with UTF-8
+	}
+	fflush(stdout);
+}
+
+// print the contents of a buffer to stdout
+void text_buffer_print(TextBuffer *buffer) {
+	text_buffer_print_internal(buffer, false);
+}
+
+// print the contents of a buffer to stdout, along with debugging information
+void text_buffer_print_debug(TextBuffer *buffer) {
+	text_buffer_print_internal(buffer, true);
+}
+
+// Does not free the pointer `buffer` (buffer might not have even been allocated with malloc)
+void text_buffer_free(TextBuffer *buffer) {
+	TextBlock *blocks = buffer->blocks;
+	u32 nblocks = buffer->nblocks;
+	for (u32 i = 0; i < nblocks; ++i) {
+		free(blocks[i].contents);
+	}
+	free(blocks);
+}
-- 
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