new file mode 100644
--- /dev/null
+++ b/fmgen/op.h
@@ -0,0 +1,135 @@
+#ifndef FM_OP_H
+#define FM_OP_H
+
+#include <stdint.h>
+#define false 0
+#define true 1
+#define Max(a,b) ((a>b)?a:b)
+#define Min(a,b) ((a<b)?a:b)
+
+//  Types ----------------------------------------------------------------
+typedef int32_t         Sample;
+typedef int32_t         ISample;
+
+// ---------------------------------------------------------------------------
+// Various implementation-specific constants.
+// Most are used to either define the bit-width of counters, or the size
+// of various constant tables.
+//
+#define FM_LFOBITS      8
+#define FM_TLBITS       7
+#define FM_TLENTS       (1 << FM_TLBITS)
+#define FM_LFOENTS      (1 << FM_LFOBITS)
+#define FM_TLPOS        (FM_TLENTS/4)
+#define FM_CLENTS       (0xc00 << 2)
+#define FM_OPSINBITS    10
+#define FM_OPSINENTS    (1 << FM_OPSINBITS)
+#define FM_EGBITS       16
+#define FM_EGCBITS      18
+#define FM_LFOCBITS     14
+#define FM_PGBITS       9
+#define FM_RATIOBITS    12
+
+typedef uint32_t uint;
+typedef enum _EGPhase { next, attack, decay, sustain, release, off } EGPhase;
+
+static inline int Limit(int v, int max, int min)
+{
+    return v > max ? max : (v < min ? min : v);
+}
+
+//  Operator ----------------------------------------------------------------
+typedef struct _FMOperator
+{
+    int32_t out, out2;
+
+    //  Phase Generator -----------------------------------------------------
+    uint32_t dp;        // Octave (used to define note in conjunction with bn, below).
+    uint8_t detune;     // Detune
+    uint8_t multiple;   // Multiple
+    uint32_t    pgcount;    // Phase generator sweep value. Only the top 9 bits are relevant/used.
+    uint32_t    pgdcount;   // Phase generator increment-per-clock value. Hopefully self-explanatory.
+    uint32_t    pgdcountl;  // Phase generator detune increment value. Used in the implementation of vibrato.
+                            // Equal to pgdcount >> 11.
+
+    //  Envelope Generator --------------------------------------------------
+    uint32_t bn;         // Block/Note
+    uint32_t egout;
+    int      eglevel;    // EG ¤Î½ÐÎÏÃÍ
+    int      eglvnext;   // ¼¡¤Î phase ¤Ë°Ü¤ëÃÍ
+    int32_t  egstep;     // EG ¤Î¼¡¤ÎÊѰܤޤǤλþ´Ö
+    int32_t  egstepd;    // egstep ¤Î»þ´Öº¹Ê¬
+    uint8_t  egtransa;   // EG ÊѲ½¤Î³ä¹ç (for attack)
+    uint8_t  egtransd;   // EG ÊѲ½¤Î³ä¹ç (for decay)
+
+    uint32_t ksr;        // key scale rate
+    EGPhase phase;
+    uint8_t ams;
+    uint8_t ms;
+
+    uint8_t keyon;      // current key state
+
+    uint8_t tl;         // Total Level   (0-127)
+    uint8_t tll;        // Total Level Latch (for CSM mode)
+    uint8_t ar;         // Attack Rate   (0-63)
+    uint8_t dr;         // Decay Rate    (0-63)
+    uint8_t sr;         // Sustain Rate  (0-63)
+    uint8_t sl;         // Sustain Level (0-127)
+    uint8_t rr;         // Release Rate  (0-63)
+    uint8_t ks;         // Keyscale      (0-3)
+    uint8_t ssgtype;    // SSG-Type Envelope Control
+
+    uint8_t amon;       // enable Amplitude Modulation
+    uint8_t paramchanged;   // Set whenever f-number or any ADSR constants
+                            // are set in OPNASetReg(), as well as upon
+                            // chip reset and chip "DAC" samplerate change.
+                            // Causes the envelope generator to reset its
+                            // internal state, also sets correct increments
+                            // for the phase generator.
+    uint8_t mute;
+} FMOperator;
+
+//  4-op Channel ------------------------------------------------------------
+typedef struct Channel4
+{
+    uint32_t fb;
+    int     buf[4];
+    uint8_t idx[6];
+    int *pms;
+    FMOperator op[4];
+} Channel4;
+
+//  OPNA Rhythm Generator ---------------------------------------------------
+typedef struct Rhythm {
+    uint8_t pan;        
+    int8_t  level;      
+    int8_t  volume;     
+    int8_t*     sample;     // Rhythm sample data
+    uint32_t    size;       // Rhythm sample data size
+    uint32_t    pos;        // Current index into rhytm sample data array
+    uint32_t    step;       // Amount to increment the above by every time
+                            // RhythmMix() gets called.
+    uint32_t    rate;       // Samplerate of rhythm sample data
+                            // (44100Hz in this implementation).
+} Rhythm;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// --------------------------------------------------------------------------
+// Miscellaneous and probably irrelevant function prototypes.
+void MakeTable(void);
+void OperatorInit(FMOperator *op);
+void OperatorReset(FMOperator *op);
+void OperatorPrepare(FMOperator *op);
+
+static inline uint32_t IsOn(FMOperator *op) {
+    return (op->phase - off);
+}
+
+#ifdef __cplusplus
+};
+#endif
+
+#endif