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// Copyright ©2017 The bíogo Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package itf8 provides ITF-8 integer encoding.
//
// ITF-8 integer encoding is specified in the CRAM format specification
// section 2.3.
package itf8
import "math/bits"
// Len returns the number of bytes required to encode u.
func Len(v int32) int {
u := uint32(v)
switch {
case u < 0x80:
return 1
case u < 0x4000:
return 2
case u < 0x200000:
return 3
case u < 0x10000000:
return 4
default:
return 5
}
}
// Decode decodes the ITF-8 encoding in b and returns the int32 value, its
// width in bytes and whether the decoding was successful. If the encoding
// is invalid, the expected length of b and false are returned. If b has zero
// length, zero, zero and false are returned.
func Decode(b []byte) (v int32, n int, ok bool) {
if len(b) == 0 {
return 0, 0, false
}
n = bits.LeadingZeros8(^(b[0] & 0xf0)) + 1
if len(b) < n {
return 0, n, false
}
switch n {
case 1:
v = int32(b[0])
case 2:
v = int32(b[1]) | int32(b[0]&0x3f)<<8
case 3:
v = int32(b[2]) | int32(b[1])<<8 | int32(b[0]&0x1f)<<16
case 4:
v = int32(b[3]) | int32(b[2])<<8 | int32(b[1])<<16 | int32(b[0]&0x0f)<<24
case 5:
v = int32(b[4]&0x0f) | int32(b[3])<<4 | int32(b[2])<<12 | int32(b[1])<<20 | int32(b[0]&0x0f)<<28
}
return v, n, true
}
// Encode encodes v as an ITF-8 into b, which must be large enough, and
// and returns the number of bytes written.
func Encode(b []byte, v int32) int {
u := uint32(v)
switch {
case u < 0x80:
b[0] = byte(u)
return 1
case u < 0x4000:
_ = b[1]
b[0] = byte(u>>8)&0x3f | 0x80
b[1] = byte(u)
return 2
case u < 0x200000:
_ = b[2]
b[0] = byte(u>>16)&0x1f | 0xc0
b[1] = byte(u >> 8)
b[2] = byte(u)
return 3
case u < 0x10000000:
_ = b[3]
b[0] = byte(u>>24)&0x0f | 0xe0
b[1] = byte(u >> 16)
b[2] = byte(u >> 8)
b[3] = byte(u)
return 4
default:
_ = b[4]
b[0] = byte(u>>28) | 0xf0
b[1] = byte(u >> 20)
b[2] = byte(u >> 12)
b[3] = byte(u >> 2)
b[4] = byte(u)
return 5
}
}
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