基本信息:
- 专利标题： 基本函數之高準確度預估
- 专利标题（英）：High accuracy estimates of elementary functions
- 专利标题（中）：基本函数之高准确度预估
- 申请号：TW087109037 申请日：1998-06-08
- 公开(公告)号：TW434507B 公开(公告)日：2001-05-16
- 发明人： 馬汀史丹利史奇摩勒 , 都諾諾曼先濟
- 申请人： 萬國商業機器公司
- 申请人地址： 美國
- 专利权人： 萬國商業機器公司
- 当前专利权人： 萬國商業機器公司
- 当前专利权人地址： 美國
- 代理人： 陳長文
- 优先权： 美國 09/017,233 19980202
- 主分类号： G06F
- IPC分类号： G06F
An improved method of estimating the square root, reciprocal square root, and reciprocal of an input value in a computer system. The input value, after being normalized, is used to select a pair of constants from a table. The constants are based on a linear approximation of the function for each interval of the input value, offset to reduce a maximum error value for a given interval. The estimated function is calculated by adding or subtracting the product of a part of the normalized input value and the first constant from the second constant. In one implementation, the input value is normalized within the range 1 ≤ x < 2, and one lookup table is used, having an interval size of 1/32. In a further preferred embodiment, only a lower order part of the mantissa is used in the multiply-add operation, to reduce the number of bits required (the high order part of the mantissa is used to select the constants from the table). In another implementation, the input value is normalized within the range 0.5 ≤ x < 2, and two lookup tables are used, a first table having an interval size of 1/32 for the range 0.5 ≤ x < 1, and a second table having an interval size of 1/16 for the range 1 ≤ x < 2.