[PATCH v3 2/6] decimal: fix encoding numbers with positive exponent.

[Serge Petrenko <sergepetrenko@tarantool.org>]

When a number having a positive exponent is encoded, the internal
decPackedFromNumber function returns a negative scale, which differs
from the scale, returned by decimal_scale(). This leads to errors in
decoding. Account for negative scale in decimal_pack() and
decimal_unpack().

Follow-up #692
---
 src/lib/core/decimal.c   | 42 ++++++++++++++++++++++++++++++++--------
 test/unit/decimal.c      | 15 ++++++++++++--
 test/unit/decimal.result | 11 ++++++++---
 3 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/src/lib/core/decimal.c b/src/lib/core/decimal.c
index e141a91f8..356acf6f2 100644
--- a/src/lib/core/decimal.c
+++ b/src/lib/core/decimal.c
@@ -33,6 +33,7 @@
 #include "third_party/decNumber/decContext.h"
 #include "third_party/decNumber/decPacked.h"
 #include "lib/core/tt_static.h"
+#include "lib/msgpuck/msgpuck.h"
 #include <stddef.h>
 #include <stdlib.h>
 #include <float.h> /* DBL_DIG */
@@ -339,20 +340,27 @@ decimal_sqrt(decimal_t *res, const decimal_t *lhs)
 uint32_t
 decimal_len(const decimal_t *dec)
 {
-	/* 1  + ceil((digits + 1) / 2) */
-	return 2 + dec->digits / 2;
+	uint32_t sizeof_scale = dec->exponent > 0 ? mp_sizeof_int(-dec->exponent) :
+						    mp_sizeof_uint(-dec->exponent);
+	/* sizeof_scale  + ceil((digits + 1) / 2) */
+	return sizeof_scale + 1 + dec->digits / 2;
 }
 
 char *
 decimal_pack(char *data, const decimal_t *dec)
 {
 	uint32_t len = decimal_len(dec);
-	*data++ = decimal_scale(dec);
-	len--;
+	char *svp = data;
+	/* encode scale */
+	if (dec->exponent > 0) {
+		data = mp_encode_int(data, -dec->exponent);
+	} else {
+		data = mp_encode_uint(data, -dec->exponent);
+	}
+	len -= data - svp;
 	int32_t scale;
 	char *tmp = (char *)decPackedFromNumber((uint8_t *)data, len, &scale, dec);
 	assert(tmp == data);
-	assert(scale == (int32_t)decimal_scale(dec));
 	(void)tmp;
 	data += len;
 	return data;
@@ -361,12 +369,30 @@ decimal_pack(char *data, const decimal_t *dec)
 decimal_t *
 decimal_unpack(const char **data, uint32_t len, decimal_t *dec)
 {
-	int32_t scale = *((*data)++);
-	len--;
+	int32_t scale;
+	const char *svp = *data;
+	if (mp_typeof(**data) == MP_UINT) {
+		scale = mp_decode_uint(data);
+	} else if (mp_typeof(**data) == MP_INT) {
+		scale = mp_decode_int(data);
+	} else {
+		return NULL;
+	}
+	/*
+	 * scale = -exponent. The exponent should be in range
+	 * [-DECIMAL_MAX_DIGITS; DECIMAL_MAX_DIGITS)
+	 */
+	if (scale > DECIMAL_MAX_DIGITS ||
+	    scale <= -DECIMAL_MAX_DIGITS) {
+		*data = svp;
+		return NULL;
+	}
+
+	len -= *data - svp;
 	decimal_t *res = decPackedToNumber((uint8_t *)*data, len, &scale, dec);
 	if (res)
 		*data += len;
 	else
-		(*data)--;
+		*data = svp;
 	return res;
 }
diff --git a/test/unit/decimal.c b/test/unit/decimal.c
index b587e1f14..b55333ed7 100644
--- a/test/unit/decimal.c
+++ b/test/unit/decimal.c
@@ -91,7 +91,7 @@ char buf[32];
 static int
 test_pack_unpack(void)
 {
-	plan(146);
+	plan(151);
 
 	test_decpack("0");
 	test_decpack("-0");
@@ -112,13 +112,24 @@ test_pack_unpack(void)
 	test_decpack("99999999999999999999999999999999999999");
 	test_decpack("-99999999999999999999999999999999999999");
 
+	/* Check correct encoding of positive exponent numbers. */
+	decimal_t dec, d1;
+	decimal_from_string(&dec, "1e10");
+	uint32_t l1 = decimal_len(&dec);
+	ok(l1 == 2, "decimal_len() is small for positive exponent decimal");
+	char *b1 = decimal_pack(buf, &dec);
+	is(b1, buf + l1, "positive exponent decimal length");
+	const char *b2 = buf;
+	is(decimal_unpack(&b2, l1, &d1), &d1, "decimal_unpack() of a positive exponent decimal");
+	is(b1, b2, "decimal_unpack uses every byte packed by decimal_pack");
+	is(decimal_compare(&dec, &d1), 0, "positive exponent number is packed/unpacked correctly");
+
 	/* Pack an invalid decimal. */
 	char *b = buf;
 	*b++ = 1;
 	*b++ = '\xab';
 	*b++ = '\xcd';
 	const char *bb = buf;
-	decimal_t dec;
 	is(decimal_unpack(&bb, 3, &dec), NULL, "unpack malformed decimal fails");
 	is(bb, buf, "decode malformed decimal preserves buffer position");
 
diff --git a/test/unit/decimal.result b/test/unit/decimal.result
index 1c72cdfab..2dd91af49 100644
--- a/test/unit/decimal.result
+++ b/test/unit/decimal.result
@@ -277,7 +277,7 @@ ok 275 - decimal_from_string(-1)
 ok 276 - decimal_log10(-1) - error on wrong operands.
 ok 277 - decimal_from_string(-10)
 ok 278 - decimal_sqrt(-10) - error on wrong operands.
-    1..146
+    1..151
     ok 1 - decimal_len(0)
     ok 2 - decimal_len(0) == len(decimal_pack(0)
     ok 3 - decimal_unpack(decimal_pack(0))
@@ -422,6 +422,11 @@ ok 278 - decimal_sqrt(-10) - error on wrong operands.
     ok 142 - decimal_unpack(decimal_pack(-99999999999999999999999999999999999999)) scale
     ok 143 - decimal_unpack(decimal_pack(-99999999999999999999999999999999999999)) precision
     ok 144 - str(decimal_unpack(decimal_pack(-99999999999999999999999999999999999999)) == -99999999999999999999999999999999999999
-    ok 145 - unpack malformed decimal fails
-    ok 146 - decode malformed decimal preserves buffer position
+    ok 145 - decimal_len() is small for positive exponent decimal
+    ok 146 - positive exponent decimal length
+    ok 147 - decimal_unpack() of a positive exponent decimal
+    ok 148 - decimal_unpack uses every byte packed by decimal_pack
+    ok 149 - positive exponent number is packed/unpacked correctly
+    ok 150 - unpack malformed decimal fails
+    ok 151 - decode malformed decimal preserves buffer position
 ok 279 - subtests
-- 
2.20.1 (Apple Git-117)