Monthly Archives: December 2007

为什么笔记本上没有FM调频收音机？

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上周买了一台昂达的MP4（ VX979+）作为圣诞礼物送给老婆。26万色的2.4寸TFT液晶屏（320x240分辨率），支持各种常见的音乐和视频格式，视频无需转换可直接播放，支持RM和RMVB格式，可播放Flash，提供了几款小游戏，还有FM调频立体声收音机。2GB闪存，可扩充至多4GB的TF卡。

如果你不是“村”里人，你可能想象不到，它的价格只有380元人民币，是的，只大概50美金！

我在想，为什么作为个人多媒体中心的笔记本电脑，却没有FM调频收音机呢？

Y combinator in Python

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在lambda系统中实现递归，需要借用Y组合算子（combinator）。下面是Python中的一个实作。

Y = lambda F: (lambda f: F(lambda x: f(f)(x))) (lambda f: F(lambda x: f(f)(x)))
F = lambda f: (lambda x: 1 if x==0 else x*f(x-1))
fact = Y(F)
print fact(10)

感觉这个Y combinator实在是令人头晕目眩，不知所以。具体的推导过程和相关理论，请参见刘未鹏先生的宏文，以及负暄琐话相关的blog（1、2）。读了几遍，仍然只是朦朦胧胧地明白了一点点，特别是后面的对角线，再读、再读... ...

My first invention disclosure got approved!

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After several months since I submitted my first invention disclosure (SUN080023), I saw there was $200 for "patent bonus" on my payroll of last month. And later received a notification email from the attorney, said my invention disclosure "was reviewed, and will not file a patent application".

While I'm not sure, if "reviewed" means "reviewed and approved"? After several rounds of email communication with the attorney, I confirmed, yes, it's approved, and that's why I got the bonus.

I heard that the  "idt tool" will support checking status (such as PENDING, REJECTED, APPROVED, READY-TO-PATENT etc). And this would happen in the next 6 months.

Python: mmap and array

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我需要在Python程序中存取一个很大的数组，数组的每一项是(int, int, float, int)的记录。如果直接用list来存放，占据的内存巨大（因为不仅所有这些数都是对象，且tuple本身也是对象）。Python提供了一个array模块，以更有效地存取数字值，但是它只支持单一的数据类型，例如你无法创建这样的array对象：a = array.array('2lfl')。

我想到了存放在文件中，并用mmap的方式来访问。除了mmap，我不知道Python中是否还有其他方法可以得到一块raw的内存。且mmap在性能和效率上，有一定的优越性。最后，辗转得到了下面的代码：

class MMArray:
    __file = __mem = None
    __realsize = __capsize = 0
    def __init__(self, type='B', fname=None, capsize=1024*1024):
        self.__elmsize = struct.calcsize(type)
        if not fname:
            fno, self.__fname = tempfile.mkstemp("-mmarray", "pyslm-")
            self.__file = os.fdopen (fno, "w+")
            self.__enlarge(capsize)
        else:
            self.fromfile(fname)
    def fromfile(self, fname):
        if not os.path.exists(fname):
            raise "The file '%s' does not exist!"
        fsize = os.path.getsize(fname)
        if fsize == 0:
            raise "The size of file '%s' is zero!" % fname
        if self.__mem: self.__mem.close()
        if self.__file: self.__file.close()
        self.__file = open (fname, "r+")
        self.__mem = mmap.mmap(self.__file.fileno(), fsize)
        self.__realsize = self.__capsize = fsize/self.__elmsize
    def tofile(self, fname):
        if fname == self.__file.name:
            raise "Can not dump the array to currently mapping file!"
        tf = open(fname, "w+")
        bsize = self.__realsize * self.__elmsize
        tf.write (self.__mem[:bsize])
        tf.close()
    def __enlarge(self, capsize):
        if self.__capsize >= capsize:
            return
        self.__capsize = capsize
        self.__file.seek(self.__elmsize * self.__capsize - 1)
        self.__file.write('')
        self.__file.flush()
        if (self.__mem): self.__mem.close()
        self.__mem = mmap.mmap(self.__file.fileno(), self.__file.tell())
    def __del__ (self):
        bsize = self.__realsize * self.__elmsize
        self.__file.truncate (bsize)
        self.__file.close()
        if self.__mem: self.__mem.close()
        os.remove(self.__fname)
    def __getitem__(self, idx):
        if idx < 0 or idx >= self.__realsize:
            raise IndexError
        return self.__access(idx)
    def __setitem__(self, idx, buf):
        if idx < 0 or idx >= self.__realsize:
            raise IndexError
        if type(buf) != type("") or len(buf) != self.__elmsize:
            raise "Not a string, or the buffer size is incorrect!"
        self.__access(idx, buf)
    def __access (self, idx, buf=None):
        start = idx * self.__elmsize
        end = start + self.__elmsize
        if not buf: return self.__mem[start:end]
        self.__mem[start:end] = buf
    def size(self):
        return self.__realsize
    def append(self, buf):
        if type(buf) != type("") or len(buf) != self.__elmsize:
            raise "Not a string, or the buffer size is incorrect!"
        if self.__realsize >= self.__capsize:
            self.__enlarge(self.__capsize*2)
        self.__access(self.__realsize, buf)
        self.__realsize += 1
    def __iter__(self):
        for i in xrange(0, self.__realsize):
            yield self.__access(i)
    def truncate(self, tsize):
        if self.__realsize >= tsize:
            self.__realsize = tsize

当然，还有许多要改进的地方，例如支持从尾部索引（即index<0），以及slicing等等。