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docs/exploring_c_prng.cpp

@@ -0,0 +1,38 @@
+void __cdecl srand( unsigned int seed )
+{
+	_getptd()->_holdrand = (unsigned long)seed;
+}
+
+int __cdecl rand( void )
+{
+	_ptiddata ptd = _getptd();
+	return( ((ptd->_holdrand = ptd->_holdrand * 214013L + 2531011L) >> 16) & 0x7fff );
+}
+
+public rand
+rand proc near
+call    sub_77C29F25     // _getptd()?
+mov     ecx, [eax+14h]   // offset of _holdrand?
+imul    ecx, 343FDh      // 214013
+add     ecx, 269EC3h     // 2531011
+mov     [eax+14h], ecx   
+mov     eax, ecx
+shr     eax, 10h         // >> 16
+and     eax, 7FFFh
+retn
+rand endp
+
+public srand
+srand proc near
+
+arg_0= dword ptr  8
+
+mov     edi, edi            // 3 lines - BP-based frame
+push    ebp
+mov     ebp, esp
+call    sub_77C29F25        // _getptd()?
+mov     ecx, [ebp+arg_0]    // ecx = seed (argument 0)
+mov     [eax+14h], ecx      // _getptd()->_holdrand = seed
+pop     ebp
+retn
+srand endp