From 5ce137a2c7f9bdea70a7222ade9e99a069226b9d Mon Sep 17 00:00:00 2001
From: Iru Cai <mytbk920423@gmail.com>
Date: Tue, 20 Nov 2018 11:47:58 +0800
Subject: add mt19937 code

---
 source/pdf/pdf-crypt.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)

diff --git a/source/pdf/pdf-crypt.c b/source/pdf/pdf-crypt.c
index b9cbc05f..cc333039 100644
--- a/source/pdf/pdf-crypt.c
+++ b/source/pdf/pdf-crypt.c
@@ -2,6 +2,109 @@
 #include "mupdf/pdf.h"
 
 #include <string.h>
+#include <stdint.h>
+
+typedef struct
+{
+	int n;
+	uint32_t MT[1248];
+	uint32_t cc;
+} mt19937;
+
+static void fcn_40c060(mt19937 *ctx)
+{
+	uint32_t *edi = &ctx->MT[624];
+	uint32_t eax, ecx, edx;
+
+	for (int i = 0; i < 227; i++) {
+		edx = ((edi[i] ^ edi[i + 1]) & 0x7fffffff) ^ edi[i];
+		if (edx & 1) {
+			eax = 0x9908b0df;
+		} else {
+			eax = 0;
+		}
+		edx >>= 1;
+		edi[i - 624] = eax ^ edi[i + 397] ^ edx;
+	}
+
+	uint32_t *esi = &ctx->MT[851];
+
+	for (int i = 0; i < 396; i++) {
+		ecx = ((esi[i] ^ esi[i + 1]) & 0x7fffffff) ^ esi[i];
+
+		if (ecx & 1) {
+			eax = 0x9908b0df;
+		} else {
+			eax = 0;
+		}
+		ecx >>= 1;
+		esi[i - 624] = eax ^ esi[i - 851] ^ ecx;
+	}
+
+	ecx = ((ctx->MT[1247] ^ ctx->MT[0]) & 0x7fffffff) ^ ctx->MT[1247];
+	if (ecx & 1) {
+		eax = 0x9908b0df;
+	} else {
+		eax = 0;
+	}
+	ecx >>= 1;
+	ctx->MT[623] = eax ^ ctx->MT[396] ^ ecx;
+	ctx->n = 0;
+}
+
+static void fcn_40c120(mt19937* ctx)
+{
+	uint32_t *mt = ctx->MT;
+	uint32_t ecx, edx;
+
+	for (int i = 0; i < 624; i++) {
+		edx = ((mt[i] ^ mt[i + 1]) & 0x7fffffff) ^ mt[i];
+
+		if (edx & 1) {
+			ecx = 0x9908b0df;
+		} else {
+			ecx = 0;
+		}
+		edx >>= 1;
+
+		ecx ^= mt[i + 397];
+		ecx ^= edx;
+
+		mt[i + 624] = ecx;
+	}
+}
+
+uint32_t mt19937_next(mt19937 *ctx)
+{
+	int n = ctx->n;
+	uint32_t eax, edx;
+
+	if (n == 624) {
+		fcn_40c120(ctx);
+	} else if (n >= 1248) {
+		fcn_40c060(ctx);
+	}
+	ctx->n++;
+
+	edx = ctx->MT[n] ^ (ctx->cc & (ctx->MT[n] >> 11));
+	eax = (edx & 0xff3a58ad) << 7;
+	edx ^= eax;
+	eax = (edx & 0xffffdf8c) << 15;
+	edx ^= eax;
+	eax = edx >> 18;
+	return eax ^ edx;
+}
+
+void mt19937_init(mt19937 *ctx, uint32_t seed)
+{
+	ctx->n = 624;
+	ctx->cc = ~0;
+
+	ctx->MT[0] = seed;
+	for (int i = 1; i < 624; i++) {
+		ctx->MT[i] = 0x6c078965 * (ctx->MT[i] ^ (ctx->MT[i-1] >> 30)) + i;
+	}
+}
 
 enum
 {
-- 
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