reduce allocations when binding string/time args

This commit reduces the number of allocations required to bind args by
eliminating string to byte slice conversions for string and time.Time
types and by only checking for bind parameters if any of the
driver.NamedValue args are named.

goos: darwin
goarch: arm64
pkg: github.com/mattn/go-sqlite3
cpu: Apple M1 Max
                           │  b.10.txt   │             x7.10.txt              │
                           │   sec/op    │   sec/op     vs base               │
CustomFunctions-10           3.230µ ± 1%   3.253µ ± 1%  +0.73% (p=0.022 n=10)
Suite/BenchmarkExec-10       1.240µ ± 0%   1.231µ ± 1%       ~ (p=0.210 n=10)
Suite/BenchmarkQuery-10      3.892µ ± 1%   3.854µ ± 1%  -0.96% (p=0.009 n=10)
Suite/BenchmarkParams-10     4.203µ ± 1%   4.163µ ± 1%  -0.94% (p=0.011 n=10)
Suite/BenchmarkStmt-10       2.814µ ± 1%   2.763µ ± 1%  -1.81% (p=0.000 n=10)
Suite/BenchmarkRows-10       131.2µ ± 1%   130.7µ ± 0%  -0.40% (p=0.035 n=10)
Suite/BenchmarkStmtRows-10   131.0µ ± 1%   128.9µ ± 1%  -1.59% (p=0.043 n=10)
geomean                      8.485µ        8.416µ       -0.82%

                           │   b.10.txt   │               x7.10.txt                │
                           │     B/op     │     B/op      vs base                  │
CustomFunctions-10             568.0 ± 0%     568.0 ± 0%        ~ (p=1.000 n=10) ¹
Suite/BenchmarkExec-10         128.0 ± 0%     128.0 ± 0%        ~ (p=1.000 n=10) ¹
Suite/BenchmarkQuery-10        688.0 ± 0%     688.0 ± 0%        ~ (p=1.000 n=10) ¹
Suite/BenchmarkParams-10      1104.0 ± 0%    1000.0 ± 0%   -9.42% (p=0.000 n=10)
Suite/BenchmarkStmt-10         920.0 ± 0%     816.0 ± 0%  -11.30% (p=0.000 n=10)
Suite/BenchmarkRows-10       9.305Ki ± 0%   9.305Ki ± 0%        ~ (p=1.000 n=10) ¹
Suite/BenchmarkStmtRows-10   9.289Ki ± 0%   9.289Ki ± 0%        ~ (p=1.000 n=10) ¹
geomean                      1.215Ki        1.177Ki        -3.08%
¹ all samples are equal

                           │  b.10.txt  │              x7.10.txt              │
                           │ allocs/op  │ allocs/op   vs base                 │
CustomFunctions-10           18.00 ± 0%   18.00 ± 0%       ~ (p=1.000 n=10) ¹
Suite/BenchmarkExec-10       7.000 ± 0%   7.000 ± 0%       ~ (p=1.000 n=10) ¹
Suite/BenchmarkQuery-10      23.00 ± 0%   23.00 ± 0%       ~ (p=1.000 n=10) ¹
Suite/BenchmarkParams-10     27.00 ± 0%   25.00 ± 0%  -7.41% (p=0.000 n=10)
Suite/BenchmarkStmt-10       25.00 ± 0%   23.00 ± 0%  -8.00% (p=0.000 n=10)
Suite/BenchmarkRows-10       525.0 ± 0%   525.0 ± 0%       ~ (p=1.000 n=10) ¹
Suite/BenchmarkStmtRows-10   524.0 ± 0%   524.0 ± 0%       ~ (p=1.000 n=10) ¹
geomean                      47.41        46.33       -2.26%
¹ all samples are equal

sqlite3.go

@@ -2182,26 +2182,90 @@ func (s *SQLiteStmt) NumInput() int {
 
 var placeHolder = []byte{0}
 
+func hasNamedArgs(args []driver.NamedValue) bool {
+	for _, v := range args {
+		if v.Name != "" {
+			return true
+		}
+	}
+	return false
+}
+
 func (s *SQLiteStmt) bind(args []driver.NamedValue) error {
 	rv := C.sqlite3_reset(s.s)
 	if rv != C.SQLITE_ROW && rv != C.SQLITE_OK && rv != C.SQLITE_DONE {
 		return s.c.lastError()
 	}
 
+	if hasNamedArgs(args) {
+		return s.bindIndices(args)
+	}
+
+	for _, arg := range args {
+		n := C.int(arg.Ordinal)
+		switch v := arg.Value.(type) {
+		case nil:
+			rv = C.sqlite3_bind_null(s.s, n)
+		case string:
+			p := stringData(v)
+			rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(p)), C.int(len(v)))
+		case int64:
+			rv = C.sqlite3_bind_int64(s.s, n, C.sqlite3_int64(v))
+		case bool:
+			val := 0
+			if v {
+				val = 1
+			}
+			rv = C.sqlite3_bind_int(s.s, n, C.int(val))
+		case float64:
+			rv = C.sqlite3_bind_double(s.s, n, C.double(v))
+		case []byte:
+			if v == nil {
+				rv = C.sqlite3_bind_null(s.s, n)
+			} else {
+				ln := len(v)
+				if ln == 0 {
+					v = placeHolder
+				}
+				rv = C._sqlite3_bind_blob(s.s, n, unsafe.Pointer(&v[0]), C.int(ln))
+			}
+		case time.Time:
+			ts := v.Format(SQLiteTimestampFormats[0])
+			p := stringData(ts)
+			rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(p)), C.int(len(ts)))
+		}
+		if rv != C.SQLITE_OK {
+			return s.c.lastError()
+		}
+	}
+	return nil
+}
+
+func (s *SQLiteStmt) bindIndices(args []driver.NamedValue) error {
+	// Find the longest named parameter name.
+	n := 0
+	for _, v := range args {
+		if m := len(v.Name); m > n {
+			n = m
+		}
+	}
+	buf := make([]byte, 0, n+2) // +2 for placeholder and null terminator
+
 	bindIndices := make([][3]int, len(args))
-	prefixes := []string{":", "@", "$"}
 	for i, v := range args {
 		bindIndices[i][0] = args[i].Ordinal
 		if v.Name != "" {
-			for j := range prefixes {
-				cname := C.CString(prefixes[j] + v.Name)
-				bindIndices[i][j] = int(C.sqlite3_bind_parameter_index(s.s, cname))
-				C.free(unsafe.Pointer(cname))
+			for j, c := range []byte{':', '@', '$'} {
+				buf = append(buf[:0], c)
+				buf = append(buf, v.Name...)
+				buf = append(buf, 0)
+				bindIndices[i][j] = int(C.sqlite3_bind_parameter_index(s.s, (*C.char)(unsafe.Pointer(&buf[0]))))
 			}
 			args[i].Ordinal = bindIndices[i][0]
 		}
 	}
 
+	var rv C.int
 	for i, arg := range args {
 		for j := range bindIndices[i] {
 			if bindIndices[i][j] == 0 {
@@ -2212,20 +2276,16 @@ func (s *SQLiteStmt) bind(args []driver.NamedValue) error {
 			case nil:
 				rv = C.sqlite3_bind_null(s.s, n)
 			case string:
-				if len(v) == 0 {
-					rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(&placeHolder[0])), C.int(0))
-				} else {
-					b := []byte(v)
-					rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(&b[0])), C.int(len(b)))
-				}
+				p := stringData(v)
+				rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(p)), C.int(len(v)))
 			case int64:
 				rv = C.sqlite3_bind_int64(s.s, n, C.sqlite3_int64(v))
 			case bool:
+				val := 0
 				if v {
-					rv = C.sqlite3_bind_int(s.s, n, 1)
-				} else {
-					rv = C.sqlite3_bind_int(s.s, n, 0)
+					val = 1
 				}
+				rv = C.sqlite3_bind_int(s.s, n, C.int(val))
 			case float64:
 				rv = C.sqlite3_bind_double(s.s, n, C.double(v))
 			case []byte:
@@ -2239,8 +2299,9 @@ func (s *SQLiteStmt) bind(args []driver.NamedValue) error {
 					rv = C._sqlite3_bind_blob(s.s, n, unsafe.Pointer(&v[0]), C.int(ln))
 				}
 			case time.Time:
-				b := []byte(v.Format(SQLiteTimestampFormats[0]))
-				rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(&b[0])), C.int(len(b)))
+				ts := v.Format(SQLiteTimestampFormats[0])
+				p := stringData(ts)
+				rv = C._sqlite3_bind_text(s.s, n, (*C.char)(unsafe.Pointer(p)), C.int(len(ts)))
 			}
 			if rv != C.SQLITE_OK {
 				return s.c.lastError()