Python 中十六进制字符串到有符号 int

发布于 2024-11-25 03:54:43 字数 433 浏览 0 评论 0原文

如何在 Python 3 中将十六进制字符串转换为有符号整型？

我能想到的最好的办法

h = '9DA92DAB'
b = bytes(h, 'utf-8')
ba = binascii.a2b_hex(b)
print(int.from_bytes(ba, byteorder='big', signed=True))

是有更简单的方法吗？无符号更容易： int(h, 16)

顺便说一句，问题的起源是 itunes 持久 id - 音乐库 xml 版本和 iTunes 十六进制版本

原文

How do I convert a hex string to a signed int in Python 3?

The best I can come up with is

h = '9DA92DAB'
b = bytes(h, 'utf-8')
ba = binascii.a2b_hex(b)
print(int.from_bytes(ba, byteorder='big', signed=True))

Is there a simpler way? Unsigned is so much easier: int(h, 16)

BTW, the origin of the question is itunes persistent id - music library xml version and iTunes hex version

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往日情怀 2024-12-02 03:54:43

在 n 位二进制补码中，位具有值：

位 0 = 2⁰
位 1 = 2¹
位 n-2 = 2^n-2
位 n-1 = -2^n-1

但位 n-1 在无符号时值为 2^n-1，因此数字为 2ⁿ > 太高。如果设置了位 n-1，则减去 2ⁿ：

def twos_complement(hexstr, bits):
    value = int(hexstr, 16)
    if value & (1 << (bits - 1)):
        value -= 1 << bits
    return value

print(twos_complement('FFFE', 16))
print(twos_complement('7FFF', 16))
print(twos_complement('7F', 8))
print(twos_complement('FF', 8))

输出：

In n-bit two's complement, bits have value:

bit 0 = 2⁰
bit 1 = 2¹
bit n-2 = 2^n-2
bit n-1 = -2^n-1

But bit n-1 has value 2^n-1 when unsigned, so the number is 2ⁿ too high. Subtract 2ⁿ if bit n-1 is set:

def twos_complement(hexstr, bits):
    value = int(hexstr, 16)
    if value & (1 << (bits - 1)):
        value -= 1 << bits
    return value

print(twos_complement('FFFE', 16))
print(twos_complement('7FFF', 16))
print(twos_complement('7F', 8))
print(twos_complement('FF', 8))

Output:

回复收藏 0 原文

九命猫 2024-12-02 03:54:43

import struct

对于Python 3（带有注释的帮助）：

h = '9DA92DAB'
struct.unpack('>i', bytes.fromhex(h))

对于Python 2：

h = '9DA92DAB'
struct.unpack('>i', h.decode('hex'))

或者如果它是小端：

h = '9DA92DAB'
struct.unpack('<i', h.decode('hex'))

import struct

For Python 3 (with comments' help):

h = '9DA92DAB'
struct.unpack('>i', bytes.fromhex(h))

For Python 2:

h = '9DA92DAB'
struct.unpack('>i', h.decode('hex'))

or if it is little endian:

h = '9DA92DAB'
struct.unpack('<i', h.decode('hex'))

回复收藏 0 原文

糖果控 2024-12-02 03:54:43

这是一个可用于任何大小的十六进制的通用函数：

import math

# hex string to signed integer
def htosi(val):
    uintval = int(val,16)
    bits = 4 * (len(val) - 2)
    if uintval >= math.pow(2,bits-1):
        uintval = int(0 - (math.pow(2,bits) - uintval))
    return uintval

并使用它：

h = str(hex(-5))
h2 = str(hex(-13589))
x = htosi(h)
x2 = htosi(h2)

Here's a general function you can use for hex of any size:

import math

# hex string to signed integer
def htosi(val):
    uintval = int(val,16)
    bits = 4 * (len(val) - 2)
    if uintval >= math.pow(2,bits-1):
        uintval = int(0 - (math.pow(2,bits) - uintval))
    return uintval

And to use it:

h = str(hex(-5))
h2 = str(hex(-13589))
x = htosi(h)
x2 = htosi(h2)

回复收藏 0 原文

誰認得朕 2024-12-02 03:54:43

这适用于 16 位有符号整数，您可以扩展为 32 位整数。它使用 2 的补码有符号数的基本定义。另请注意，与 1 的异或是与二进制否定相同。

# convert to unsigned
x = int('ffbf', 16) # example (-65)
# check sign bit
if (x & 0x8000) == 0x8000:
    # if set, invert and add one to get the negative value, then add the negative sign
    x = -( (x ^ 0xffff) + 1)

This works for 16 bit signed ints, you can extend for 32 bit ints. It uses the basic definition of 2's complement signed numbers. Also note xor with 1 is the same as a binary negate.

# convert to unsigned
x = int('ffbf', 16) # example (-65)
# check sign bit
if (x & 0x8000) == 0x8000:
    # if set, invert and add one to get the negative value, then add the negative sign
    x = -( (x ^ 0xffff) + 1)

回复收藏 0 原文

上课铃就是安魂曲 2024-12-02 03:54:43

这是一个很晚的答案，但这里有一个执行上述操作的函数。这将延伸到您提供的任何长度。将此部分归功于另一个 SO 答案（我丢失了链接，所以如果您找到它，请提供它）。

def hex_to_signed(source):
    """Convert a string hex value to a signed hexidecimal value.

    This assumes that source is the proper length, and the sign bit
    is the first bit in the first byte of the correct length.

    hex_to_signed("F") should return -1.
    hex_to_signed("0F") should return 15.
    """
    if not isinstance(source, str):
        raise ValueError("string type required")
    if 0 == len(source):
        raise valueError("string is empty")
    sign_bit_mask = 1 << (len(source)*4-1)
    other_bits_mask = sign_bit_mask - 1
    value = int(source, 16)
    return -(value & sign_bit_mask) | (value & other_bits_mask)

It's a very late answer, but here's a function to do the above. This will extend for whatever length you provide. Credit for portions of this to another SO answer (I lost the link, so please provide it if you find it).

def hex_to_signed(source):
    """Convert a string hex value to a signed hexidecimal value.

    This assumes that source is the proper length, and the sign bit
    is the first bit in the first byte of the correct length.

    hex_to_signed("F") should return -1.
    hex_to_signed("0F") should return 15.
    """
    if not isinstance(source, str):
        raise ValueError("string type required")
    if 0 == len(source):
        raise valueError("string is empty")
    sign_bit_mask = 1 << (len(source)*4-1)
    other_bits_mask = sign_bit_mask - 1
    value = int(source, 16)
    return -(value & sign_bit_mask) | (value & other_bits_mask)

回复收藏 0 原文

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