1package json
2
3import (
4	"unsafe"
5)
6
7var endianness int
8
9func init() {
10	var b [2]byte
11	*(*uint16)(unsafe.Pointer(&b)) = uint16(0xABCD)
12
13	switch b[0] {
14	case 0xCD:
15		endianness = 0 // LE
16	case 0xAB:
17		endianness = 1 // BE
18	default:
19		panic("could not determine endianness")
20	}
21}
22
23// "00010203...96979899" cast to []uint16
24var intLELookup = [100]uint16{
25	0x3030, 0x3130, 0x3230, 0x3330, 0x3430, 0x3530, 0x3630, 0x3730, 0x3830, 0x3930,
26	0x3031, 0x3131, 0x3231, 0x3331, 0x3431, 0x3531, 0x3631, 0x3731, 0x3831, 0x3931,
27	0x3032, 0x3132, 0x3232, 0x3332, 0x3432, 0x3532, 0x3632, 0x3732, 0x3832, 0x3932,
28	0x3033, 0x3133, 0x3233, 0x3333, 0x3433, 0x3533, 0x3633, 0x3733, 0x3833, 0x3933,
29	0x3034, 0x3134, 0x3234, 0x3334, 0x3434, 0x3534, 0x3634, 0x3734, 0x3834, 0x3934,
30	0x3035, 0x3135, 0x3235, 0x3335, 0x3435, 0x3535, 0x3635, 0x3735, 0x3835, 0x3935,
31	0x3036, 0x3136, 0x3236, 0x3336, 0x3436, 0x3536, 0x3636, 0x3736, 0x3836, 0x3936,
32	0x3037, 0x3137, 0x3237, 0x3337, 0x3437, 0x3537, 0x3637, 0x3737, 0x3837, 0x3937,
33	0x3038, 0x3138, 0x3238, 0x3338, 0x3438, 0x3538, 0x3638, 0x3738, 0x3838, 0x3938,
34	0x3039, 0x3139, 0x3239, 0x3339, 0x3439, 0x3539, 0x3639, 0x3739, 0x3839, 0x3939,
35}
36
37var intBELookup = [100]uint16{
38	0x3030, 0x3031, 0x3032, 0x3033, 0x3034, 0x3035, 0x3036, 0x3037, 0x3038, 0x3039,
39	0x3130, 0x3131, 0x3132, 0x3133, 0x3134, 0x3135, 0x3136, 0x3137, 0x3138, 0x3139,
40	0x3230, 0x3231, 0x3232, 0x3233, 0x3234, 0x3235, 0x3236, 0x3237, 0x3238, 0x3239,
41	0x3330, 0x3331, 0x3332, 0x3333, 0x3334, 0x3335, 0x3336, 0x3337, 0x3338, 0x3339,
42	0x3430, 0x3431, 0x3432, 0x3433, 0x3434, 0x3435, 0x3436, 0x3437, 0x3438, 0x3439,
43	0x3530, 0x3531, 0x3532, 0x3533, 0x3534, 0x3535, 0x3536, 0x3537, 0x3538, 0x3539,
44	0x3630, 0x3631, 0x3632, 0x3633, 0x3634, 0x3635, 0x3636, 0x3637, 0x3638, 0x3639,
45	0x3730, 0x3731, 0x3732, 0x3733, 0x3734, 0x3735, 0x3736, 0x3737, 0x3738, 0x3739,
46	0x3830, 0x3831, 0x3832, 0x3833, 0x3834, 0x3835, 0x3836, 0x3837, 0x3838, 0x3839,
47	0x3930, 0x3931, 0x3932, 0x3933, 0x3934, 0x3935, 0x3936, 0x3937, 0x3938, 0x3939,
48}
49
50var intLookup = [2]*[100]uint16{&intLELookup, &intBELookup}
51
52func appendInt(b []byte, n int64) []byte {
53	return formatInteger(b, uint64(n), n < 0)
54}
55
56func appendUint(b []byte, n uint64) []byte {
57	return formatInteger(b, n, false)
58}
59
60func formatInteger(out []byte, n uint64, negative bool) []byte {
61	if !negative {
62		if n < 10 {
63			return append(out, byte(n+'0'))
64		} else if n < 100 {
65			u := intLELookup[n]
66			return append(out, byte(u), byte(u>>8))
67		}
68	} else {
69		n = -n
70	}
71
72	lookup := intLookup[endianness]
73
74	var b [22]byte
75	u := (*[11]uint16)(unsafe.Pointer(&b))
76	i := 11
77
78	for n >= 100 {
79		j := n % 100
80		n /= 100
81		i--
82		u[i] = lookup[j]
83	}
84
85	i--
86	u[i] = lookup[n]
87
88	i *= 2 // convert to byte index
89	if n < 10 {
90		i++ // remove leading zero
91	}
92	if negative {
93		i--
94		b[i] = '-'
95	}
96
97	return append(out, b[i:]...)
98}
99