hunt.for

来自「Numerical Recipes一书中例子的源码所用到的函数集,William」· FOR 代码 · 共 46 行

      SUBROUTINE hunt(xx,n,x,jlo)
      INTEGER jlo,n
      REAL x,xx(n)
      INTEGER inc,jhi,jm
      LOGICAL ascnd
      ascnd=xx(n).ge.xx(1)
      if(jlo.le.0.or.jlo.gt.n)then
        jlo=0
        jhi=n+1
        goto 3
      endif
      inc=1
      if(x.ge.xx(jlo).eqv.ascnd)then
1       jhi=jlo+inc
        if(jhi.gt.n)then
          jhi=n+1
        else if(x.ge.xx(jhi).eqv.ascnd)then
          jlo=jhi
          inc=inc+inc
          goto 1
        endif
      else
        jhi=jlo
2       jlo=jhi-inc
        if(jlo.lt.1)then
          jlo=0
        else if(x.lt.xx(jlo).eqv.ascnd)then
          jhi=jlo
          inc=inc+inc
          goto 2
        endif
      endif
3     if(jhi-jlo.eq.1)then
        if(x.eq.xx(n))jlo=n-1
        if(x.eq.xx(1))jlo=1
        return
      endif
      jm=(jhi+jlo)/2
      if(x.ge.xx(jm).eqv.ascnd)then
        jlo=jm
      else
        jhi=jm
      endif
      goto 3
      END