negative-number | 易学教程

In Python, what is a good way to round towards zero in integer division?

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问题 1/2 gives 0 as it should. However, -1/2 gives -1 , but I want it to round towards 0 (i.e. I want -1/2 to be 0), regardless of whether it's positive or negative. What is the best way to do that? 回答1: Do floating point division then convert to an int. No extra modules needed. >>> int(float(-1)/2) 0 >>> int(float(-3)/2) -1 >>> int(float(1)/2) 0 >>> int(float(3)/2) 1 回答2: Python's default division of integers is return the floor (towards negative infinity) with no ability to change that. You can

2's complement hex number to decimal in java

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问题 I have a hex string that represents a 2's complement number. Is there an easy way (libraries/functions) to translate the hex into a decimal without working directly with its bits?? E.G. This is the expected output given the hex on the left: "0000" => 0 "7FFF" => 32767 (max positive number) "8000" => -32768 (max negative number) "FFFF" => -1 Thanks! 回答1: This seems to trick java into converting the number without forcing a positive result: Integer.valueOf("FFFF",16).shortValue(); // evaluates

Distinguish zero and negative zero

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问题 I have run into a situation in my code where a function returns a double, and it is possible for this double to be a zero, a negative zero, or another value entirely. I need to distinguish between zero and negative zero, but the default double comparison does not. Due to the format of doubles, C++ does not allow for comparison of doubles using bitwise operators, so I am unsure how to procede. How can I distinguish between the two? 回答1: Call std::signbit() to determine the state of the sign

processing negative number in “accounting” format

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I have dataset, which negative value is presented with a bracket around the number i.e. (10)==-10 , it is in csv format, how can I process it so that R will interpret the (10) as -10 ? Thank you. UPDATE I know I can work it out by replacing ( as - , remove ) , and use as.numeric afterwards, but is there a more elegant way for this issue? If you create an "as.acntngFmt" method for the accounting format, you can read (or perhaps re-read with a text connection using colClasses("acnt"). setClass("acntngFmt") # [1] "acntngFmt" setAs("character", "acntngFmt", function(from) as.numeric( gsub("\\)", "

Java: right shift on negative number

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I am very confused on right shift operation on negative number, here is the code. int n = -15; System.out.println(Integer.toBinaryString(n)); int mask = n >> 31; System.out.println(Integer.toBinaryString(mask)); And the result is: 11111111111111111111111111110001 11111111111111111111111111111111 Why right shifting a negative number by 31 not 1 (the sign bit)? Alvin Wong Because in Java there are no unsigned datatypes, there are two types of right shifts: arithmetic shift >> and logical shift >>> . http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html Arithmetic shift >> will keep

Floats not evaluating as negative (Python)

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问题 I am trying to delete floating point values in a list that are negative. The original list with all of the values looks like this: [ 0.030079979253112028, -0.006015995850622406, -0.08920269709543568, -25.72356846473029, -9.770807053941908, -66.38340248962655, -188.7778008298755, -165.95850622406638, 99.99, 33.81404564315352, 0.1742564315352697, -0.00560109958506224, -0.008297925311203318, -1.4044238589211617 ] After I run a for loop that says if num<0: list.remove(num) the list looks like

Representation of negative numbers in C?

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How does C represent negative integers? Is it by two's complement representation or by using the MSB (most significant bit)? -1 in hexadecimal is ffffffff . So please clarify this for me. ISO C ( C99 section 6.2.6.2/2 in this case but it carries forward to later iterations of the standard (a) ) states that an implementation must choose one of three different representations for integral data types, two's complement, ones' complement or sign/magnitude (although it's incredibly likely that the two's complement implementations far outweigh the others). In all those representations, positive

Best way to make Java's modulus behave like it should with negative numbers?

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In java when you do a % b If a is negative, it will return a negative result, instead of wrapping around to b like it should. What's the best way to fix this? Only way I can think is a < 0 ? b + a : a % b Peter Lawrey It behaves as it should a % b = a - a / b * b; i.e. it's the remainder. You can do (a % b + b) % b This expression works as the result of (a % b) is necessarily lower than b , no matter if a is positive or negative. Adding b takes care of the negative values of a , since (a % b) is a negative value between -b and 0 , (a % b + b) is necessarily lower than b and positive. The last

processing negative number in “accounting” format

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问题 I have dataset, which negative value is presented with a bracket around the number i.e. (10)==-10 , it is in csv format, how can I process it so that R will interpret the (10) as -10 ? Thank you. UPDATE I know I can work it out by replacing ( as - , remove ) , and use as.numeric afterwards, but is there a more elegant way for this issue? 回答1: If you create an "as.acntngFmt" method for the accounting format, you can read (or perhaps re-read with a text connection using colClasses("acnt").

Java: right shift on negative number

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问题 I am very confused on right shift operation on negative number, here is the code. int n = -15; System.out.println(Integer.toBinaryString(n)); int mask = n >> 31; System.out.println(Integer.toBinaryString(mask)); And the result is: 11111111111111111111111111110001 11111111111111111111111111111111 Why right shifting a negative number by 31 not 1 (the sign bit)? 回答1: Because in Java there are no unsigned datatypes, there are two types of right shifts: arithmetic shift >> and logical shift >>> .