From: Stefan Brüns <redacted>
Date: Sun, 24 Apr 2016 00:48:26 +0000 (+0200)
Subject: analog: Implement multiplication for sr_rational
X-Git-Tag: libsigrok-0.5.0~399
X-Git-Url: https://sigrok.org/gitweb/?p=libsigrok.git;a=commitdiff_plain;h=ee1b6054d6d6a00698ddae421eae63019c452b6d

analog: Implement multiplication for sr_rational
---

diff --git a/include/libsigrok/proto.h b/include/libsigrok/proto.h
index 0dd594ed..bd725057 100644
--- a/include/libsigrok/proto.h
+++ b/include/libsigrok/proto.h
@@ -34,6 +34,8 @@ SR_API int sr_analog_unit_to_string(const struct sr_datafeed_analog *analog,
 		char **result);
 SR_API void sr_rational_set(struct sr_rational *r, int64_t p, uint64_t q);
 SR_API int sr_rational_eq(const struct sr_rational *a, const struct sr_rational *b);
+SR_API int sr_rational_mult(struct sr_rational *res, const struct sr_rational *a,
+		const struct sr_rational *b);
 
 /*--- backend.c -------------------------------------------------------------*/
 
diff --git a/src/analog.c b/src/analog.c
index a04844d6..7c0dde1b 100644
--- a/src/analog.c
+++ b/src/analog.c
@@ -433,4 +433,77 @@ SR_API int sr_rational_eq(const struct sr_rational *a, const struct sr_rational
 #endif
 }
 
+/**
+ * Multiply two sr_rational
+ *
+ * @param[in] a First value
+ * @param[in] b Second value
+ * @param[out] res Result
+ *
+ * The resulting nominator/denominator are reduced if the result would not fit
+ * otherwise. If the resulting nominator/denominator are relatively prime,
+ * this may not be possible.
+ *
+ * @retval SR_OK Success.
+ * @retval SR_ERR_ARG Resulting value to large
+ *
+ * @since 0.5.0
+ */
+SR_API int sr_rational_mult(struct sr_rational *res, const struct sr_rational *a,
+	const struct sr_rational *b)
+{
+#ifdef HAVE___INT128_T
+	__int128_t p;
+	__uint128_t q;
+
+	p = (__int128_t)(a->p) * (__int128_t)(b->p);
+	q = (__uint128_t)(a->q) * (__uint128_t)(b->q);
+
+	if ((p > INT64_MAX) || (p < INT64_MIN) || (q > UINT64_MAX)) {
+		while (!((p & 1) || (q & 1))) {
+			p /= 2;
+			q /= 2;
+		}
+	}
+
+	if ((p > INT64_MAX) || (p < INT64_MIN) || (q > UINT64_MAX)) {
+		// TODO: determine gcd to do further reduction
+		return SR_ERR_ARG;
+	}
+
+	res->p = (int64_t)(p);
+	res->q = (uint64_t)(q);
+
+	return SR_OK;
+
+#else
+	struct sr_int128_t p;
+	struct sr_uint128_t q;
+
+	mult_int64(&p, a->p, b->p);
+	mult_uint64(&q, a->q, b->q);
+
+	while (!(p.low & 1) && !(q.low & 1)) {
+		p.low /= 2;
+		if (p.high & 1) p.low |= (1ll << 63);
+		p.high >>= 1;
+		q.low /= 2;
+		if (q.high & 1) q.low |= (1ll << 63);
+		q.high >>= 1;
+	}
+
+	if (q.high)
+		return SR_ERR_ARG;
+	if ((p.high >= 0) && (p.low > INT64_MAX))
+		return SR_ERR_ARG;
+	if (p.high < -1)
+		return SR_ERR_ARG;
+
+	res->p = (int64_t)p.low;
+	res->q = q.low;
+
+	return SR_OK;
+#endif
+}
+
 /** @} */
diff --git a/tests/analog.c b/tests/analog.c
index 64e355eb..b5f2beb8 100644
--- a/tests/analog.c
+++ b/tests/analog.c
@@ -225,6 +225,47 @@ START_TEST(test_cmp_rational)
 }
 END_TEST
 
+START_TEST(test_mult_rational)
+{
+	const struct sr_rational r[][3] = {
+		/*   a    *    b    =    c   */
+		{ { 1, 1 }, { 1, 1 }, { 1, 1 }},
+		{ { 2, 1 }, { 3, 1 }, { 6, 1 }},
+		{ { 1, 2 }, { 2, 1 }, { 1, 1 }},
+		/* Test negative numbers */
+		{ { -1, 2 }, { 2, 1 }, { -1, 1 }},
+		{ { -1, 2 }, { -2, 1 }, { 1, 1 }},
+		{ { -(1ll<<20), (1ll<<10) }, { -(1ll<<20), 1 }, { (1ll<<30), 1 }},
+		/* Test reduction */
+		{ { INT32_MAX, (1ll<<12) }, { (1<<2), 1 }, { INT32_MAX, (1ll<<10) }},
+		{ { INT64_MAX, (1ll<<63) }, { (1<<3), 1 }, { INT64_MAX, (1ll<<60) }},
+		/* Test large numbers */
+		{ {  (1ll<<40), (1ll<<10) }, {  (1ll<<30), 1 }, { (1ll<<60), 1 }},
+		{ { -(1ll<<40), (1ll<<10) }, { -(1ll<<30), 1 }, { (1ll<<60), 1 }},
+
+		{ { 1000, 1 }, { 8000, 1 }, { 8000000, 1 }},
+		{ { 10000, 1 }, { 80000, 1 }, { 800000000, 1 }},
+		{ { 10000*3, 4 }, { 80000*3, 1 }, { 200000000*9, 1 }},
+		{ { 1, 1000 }, { 1, 8000 }, { 1, 8000000 }},
+		{ { 1, 10000 }, { 1, 80000 }, { 1, 800000000 }},
+		{ { 4, 10000*3 }, { 1, 80000*3 }, { 1, 200000000*9 }},
+
+		{ { -10000*3, 4 }, { 80000*3, 1 }, { -200000000*9, 1 }},
+		{ { 10000*3, 4 }, { -80000*3, 1 }, { -200000000*9, 1 }},
+	};
+
+	for (unsigned i = 0; i < ARRAY_SIZE(r); i++) {
+		struct sr_rational res;
+
+		int rc = sr_rational_mult(&res, &r[i][0], &r[i][1]);
+		fail_unless(rc == SR_OK);
+		fail_unless(sr_rational_eq(&res, &r[i][2]) == 1,
+			"sr_rational_mult() failed: [%d] %ld/%lu != %ld/%lu.",
+			i, res.p, res.q, r[i][2].p, r[i][2].q);
+	}
+}
+END_TEST
+
 Suite *suite_analog(void)
 {
 	Suite *s;
@@ -240,6 +281,7 @@ Suite *suite_analog(void)
 	tcase_add_test(tc, test_set_rational);
 	tcase_add_test(tc, test_set_rational_null);
 	tcase_add_test(tc, test_cmp_rational);
+	tcase_add_test(tc, test_mult_rational);
 	suite_add_tcase(s, tc);
 
 	return s;