Commitb7f3eb3

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Add hash_combine64.

Extracted from a larger patch by Amul Sul, with some comment additionsby me.Discussion:http://postgr.es/m/20171024113004.hn5qajypin4dy5sw@alap3.anarazel.de

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Lines changed: 14 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,8 +8,8 @@`
`8`	`8`	`#defineHASHUTILS_H`
`9`	`9`
`10`	`10`	`/*`
`11`		`- * Combine two hash values, resulting in another hash value, with decent bit`
`12`		`- * mixing.`
	`11`	`+ * Combine two32-bithash values, resulting in another hash value, with`
	`12`	`+ *decent bitmixing.`
`13`	`13`	`*`
`14`	`14`	`* Similar to boost's hash_combine().`
`15`	`15`	`*/`
`@@ -20,6 +20,18 @@ hash_combine(uint32 a, uint32 b)`
`20`	`20`	`returna;`
`21`	`21`	`}`
`22`	`22`
	`23`	`+/*`
	`24`	`+ * Combine two 64-bit hash values, resulting in another hash value, using the`
	`25`	`+ * same kind of technique as hash_combine(). Testing shows that this also`
	`26`	`+ * produces good bit mixing.`
	`27`	`+ */`
	`28`	`+staticinlineuint64`
	`29`	`+hash_combine64(uint64a,uint64b)`
	`30`	`+{`
	`31`	`+/* 0x49a0f4dd15e5a8e3 is 64bit random data */`
	`32`	`+a ^=b+0x49a0f4dd15e5a8e3+ (a <<54)+ (a >>7);`
	`33`	`+returna;`
	`34`	`+}`
`23`	`35`
`24`	`36`	`/*`
`25`	`37`	`* Simple inline murmur hash implementation hashing a 32 bit integer, for`

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