fixes ValidPrintString bugs (#91)

Author: kalamay

ascii/ascii_test.go

@@ -28,6 +28,8 @@ var testStrings = [...]string{
 	"\x80",
 	"\x7F",
 	"\xFF",
+	"\x1fxxx",
+	"\x1fxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
 	"a string of 16B.",
 	"an invalid string of 32B. \x00......",
 	"some kind of long string with only ascii characters.",

ascii/valid_print.go

@@ -60,7 +60,7 @@ func ValidPrintString(s string) bool {
 	var x uint32
 	switch n {
 	case 4:
-		x = 0x20202020 | *(*uint32)(p)
+		x = *(*uint32)(p)
 	case 3:
 		x = 0x20000000 | uint32(*(*uint16)(p)) | uint32(*(*uint8)(unsafe.Pointer(uintptr(p) + 2)))<<16
 	case 2:

ascii/valid_print_amd64.s

@@ -11,7 +11,7 @@ TEXT ·validPrintAVX2(SB), NOSPLIT, $0-24
 	MOVQ $0x0000000000000000, DX
 
 	// Initialize 128 bits registers.
-	MOVQ   $0x1919191919191919, BX
+	MOVQ   $0x1F1F1F1F1F1F1F1F, BX
 	MOVQ   $0x7e7e7e7e7e7e7e7e, BP
 	PINSRQ $0x00, BX, X0
 	PINSRQ $0x01, BX, X0

ascii/valid_print_asm.go

@@ -21,7 +21,7 @@ func main() {
 	Comment("Initialize 128 bits registers.")
 	min := GP64()
 	max := GP64()
-	MOVQ(U64(0x1919191919191919), min)
+	MOVQ(U64(0x1F1F1F1F1F1F1F1F), min)
 	MOVQ(U64(0x7E7E7E7E7E7E7E7E), max)
 
 	minXMM := XMM()