我是一个新的汇编程序员，我无法成功找到一个数字有多少位数。我的目的是找到阶乘。
我在程序集8086的仿真器中编程。
最佳答案
执行此操作的最有效方法是使用bsr指令（请参见此slides，20至25）。
这应该编写如下代码：
.text
.globl main
.type main, @function
main:
movl $1024, %eax ;; pushing the integer (1024) to analyze
bsrl %eax, %eax ;; bit scan reverse (give the smallest non zero index)
inc %eax ;; taking the 0th index into account
但是，我想您需要以10为底的日志，而不是以2为底的日志...因此，这里是代码：
.text
.globl main
.type main, @function
main:
movl $1024, %eax ;; pushing the integer (1024) to analyze
bsrl %eax, %eax ;; bit scan reverse (give the smallest non zero index)
inc %eax ;; taking the 0th index into account
pushl %eax ;; saving the previous result on the stack
fildl (%esp) ;; loading the previous result to the FPU stack (st(0))
fldlg2 ;; loading log10(2) on the FPU stack
fmulp %st, %st(1) ;; multiplying %st(0) and %st(1) and storing result in %st(0)
;; We need to set the FPU control word to 'round-up' (and not 'round-down')
fstcw -2(%esp) ;; saving the old FPU control word
movw -2(%esp), %ax ;; storing the FPU control word in %ax
andw $0xf3ff, %ax ;; removing everything else
orw $0x0800, %ax ;; setting the proper bit to '1'
movw %ax, -4(%esp) ;; getting the value back to memory
fldcw -4(%esp) ;; setting the FPU control word to the proper value
frndint ;; rounding-up
fldcw -2(%esp) ;; restoring the old FPU control word
fistpl (%esp) ;; loading the final result to the stack
popl %eax ;; setting the return value to be our result
leave
ret
我很想知道是否有人能找到比这更好的选择！确实，使用SSE说明可能会有所帮助。