osd: 64x64 multiply helpers (nw)

Can we have these? I didn't attempt to add implementations for anything other than MSVC, but I believe gcc and clang for 64-bit targets have equivalents.

src/osd/eivcx86.h

@@ -403,4 +403,24 @@ static inline float _recip_approx(float z)
 }
 #endif
 
+
+/*-------------------------------------------------
+    mul_64x64 - perform a signed 64 bit x 64 bit
+    multiply and return the full 128 bit result
+-------------------------------------------------*/
+
+#ifdef PTR64
+#define mul_64x64 _mul128
+#endif
+
+
+/*-------------------------------------------------
+    mulu_64x64 - perform an unsigned 64 bit x 64
+    bit multiply and return the full 128 bit result
+-------------------------------------------------*/
+
+#ifdef PTR64
+#define mulu_64x64 _umul128
+#endif
+
 #endif // MAME_OSD_EIVCX86_H

src/osd/eminline.h

@@ -260,6 +260,62 @@ inline float recip_approx(float value)
 #endif
 
 
+/*-------------------------------------------------
+    mul_64x64 - perform a signed 64 bit x 64 bit
+    multiply and return the full 128 bit result
+-------------------------------------------------*/
+
+#ifndef mul_64x64
+inline int64_t mul_64x64(int64_t a, int64_t b, int64_t *hi)
+{
+	uint64_t const a_hi = uint32_t(a >> 32);
+	uint64_t const b_hi = uint32_t(b >> 32);
+	uint64_t const a_lo = uint32_t(a);
+	uint64_t const b_lo = uint32_t(b);
+
+	uint64_t const ab_lo = a_lo * b_lo;
+	uint64_t const ab_m1 = a_hi * b_lo;
+	uint64_t const ab_m2 = a_lo * b_hi;
+	uint64_t const ab_hi = a_hi * b_hi;
+	uint64_t const carry = ((ab_lo >> 32) + uint32_t(ab_m1) + uint32_t(ab_m2)) >> 32;
+
+	*hi = ab_hi + (ab_m1 >> 32) + (ab_m2 >> 32) + carry;
+
+	// adjust for sign
+	if (a < 0)
+		*hi -= b;
+	if (b < 0)
+		*hi -= a;
+
+	return ab_lo + (ab_m1 << 32) + (ab_m2 << 32);
+}
+#endif
+
+
+/*-------------------------------------------------
+    mulu_64x64 - perform an unsigned 64 bit x 64
+    bit multiply and return the full 128 bit result
+-------------------------------------------------*/
+
+#ifndef mulu_64x64
+inline uint64_t mulu_64x64(uint64_t a, uint64_t b, uint64_t *hi)
+{
+	uint64_t const a_hi = uint32_t(a >> 32);
+	uint64_t const b_hi = uint32_t(b >> 32);
+	uint64_t const a_lo = uint32_t(a);
+	uint64_t const b_lo = uint32_t(b);
+
+	uint64_t const ab_lo = a_lo * b_lo;
+	uint64_t const ab_m1 = a_hi * b_lo;
+	uint64_t const ab_m2 = a_lo * b_hi;
+	uint64_t const ab_hi = a_hi * b_hi;
+	uint64_t const carry = ((ab_lo >> 32) + uint32_t(ab_m1) + uint32_t(ab_m2)) >> 32;
+
+	*hi = ab_hi + (ab_m1 >> 32) + (ab_m2 >> 32) + carry;
+
+	return ab_lo + (ab_m1 << 32) + (ab_m2 << 32);
+}
+#endif
 
 /***************************************************************************
     INLINE BIT MANIPULATION FUNCTIONS