From f03e7c515d285e0efff2a09dacba48120778614a Mon Sep 17 00:00:00 2001
From: Hayden K <imaciidz@gmail.com>
Date: Tue, 11 Feb 2025 17:48:49 -0500
Subject: Add feature to remove the chat rate limit

This probably works for basically every game, but it was only tested for
L4D/L4D2/L4D:S/Portal 2.
---
 src/chatrate.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/chatrate.c

(limited to 'src')

diff --git a/src/chatrate.c b/src/chatrate.c
new file mode 100644
index 0000000..b69b0d5
--- /dev/null
+++ b/src/chatrate.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright © 2025 Hayden K <imaciidz@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "con_.h"
+#include "errmsg.h"
+#include "feature.h"
+#include "intdefs.h"
+#include "langext.h"
+#include "os.h"
+#include "x86.h"
+#include "x86util.h"
+
+FEATURE("chat rate limit removal")
+GAMESPECIFIC(L4Dbased) // Tested/known to work in L4D1/2, L4D:S, and Portal 2.
+
+static uchar *patchedbyte;
+
+// Same method as SAR here. Basically, the game only lets you chat every 0.66s.
+// So, instead of adding 0.66 to the current time, we subtract it, and that
+// means we can always chat immediately.
+
+static inline bool find_ratelimit_insn(struct con_cmd *cmd_say) {
+	// Find the add instruction
+	uchar *insns = (uchar *)cmd_say->cb;
+	for (uchar *p = insns; p - insns < 128;) {
+		// find FADD
+		if (p[0] == X86_FLTBLK5 && p[1] == X86_MODRM(0, 0, 5)) {
+			patchedbyte = p + 1;
+			return true;
+		}
+		// Portal 2, L4D2 2125-2134, L4D:S all use SSE2, so try finding ADDSD
+		if (p[0] == X86_PFX_REPN && p[1] == X86_2BYTE & p[2] == X86_2B_ADD) {
+			patchedbyte = p + 2;
+			return true;
+		}
+		NEXT_INSN(p, "chat rate limit");
+	}
+	return false;
+}
+
+static inline bool patch_ratelimit_insn() {
+	// if FADD replace with FSUB; otherwise it is ADDSD, replace that with SUBSD
+	if (!os_mprot(patchedbyte, 1, PAGE_EXECUTE_READWRITE)) {
+		errmsg_errorsys("failed to patch chat rate limit: "
+				"couldn't make memory writable");
+		return false;
+	}
+	if (*patchedbyte == X86_MODRM(0, 0, 5)) *patchedbyte = X86_MODRM(0, 4, 5);
+	else *patchedbyte = X86_2B_SUB;
+	return true;
+}
+
+static inline void unpatch_ratelimit_insn() {
+	// same logic as above but in reverse
+	if (*patchedbyte == X86_MODRM(0, 4, 5)) *patchedbyte = X86_MODRM(0, 0, 5);
+	else *patchedbyte = X86_2B_ADD;
+}
+
+INIT {
+	struct con_cmd *cmd_say = con_findcmd("say");
+	if_cold (!cmd_say) return false;
+	if (!find_ratelimit_insn(cmd_say)) {
+		errmsg_errorx("couldn't find chat rate limit instruction");
+		return FEAT_INCOMPAT;
+	}
+	if (!patch_ratelimit_insn()) {
+		errmsg_errorx("couldn't patch chat rate limit");
+		return FEAT_FAIL;
+	}
+	return FEAT_OK;
+}
+
+END {
+	unpatch_ratelimit_insn();
+}
-- 
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