From: Luke Kenneth Casson Leighton Date: Sat, 13 Apr 2019 03:55:13 +0000 (+0100) Subject: add c version from original paper X-Git-Tag: ls180-24jan2020~1235 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=3662c45c3292faab4f1803be19f3ed953ae13b0d;p=ieee754fpu.git add c version from original paper --- diff --git a/src/add/fsqrt.py b/src/add/fsqrt.py index 6b233779..d2fe0b31 100644 --- a/src/add/fsqrt.py +++ b/src/add/fsqrt.py @@ -15,7 +15,7 @@ function [15:0] sqrt; //intermediate signals. reg [31:0] a; reg [15:0] q; - reg [17:0] left,right,r; + reg [17:0] left,right,r; integer i; begin //initialize all the variables. @@ -26,7 +26,7 @@ begin right = 0; //input to adder/sub r = 0; //remainder //run the calculations for 16 iterations. - for(i=0;i<16;i=i+1) begin + for(i=0;i<16;i=i+1) begin right = {q,r[17],1'b1}; left = {r[15:0],a[31:30]}; a = {a[29:0],2'b00}; //left shift by 2 bits. @@ -34,10 +34,64 @@ begin r = left + right; else //subtract if r is positive r = left - right; - q = {q[14:0],!r[17]}; + q = {q[14:0],!r[17]}; end sqrt = q; //final assignment of output. end endfunction //end of Function + +c version (from paper linked from URL) + +unsigned squart(D, r) /*Non-Restoring sqrt*/ + unsigned D; /*D:32-bit unsigned integer to be square rooted */ + int *r; +{ + unsigned Q = 0; /*Q:16-bit unsigned integer (root)*/ + int R = 0; /*R:17-bit integer (remainder)*/ + int i; + for (i = 15;i>=0;i--) /*for each root bit*/ + { + if (R>=0) + { /*new remainder:*/ + R = R<<2)|((D>>(i+i))&3); + R = R-((Q<<2)|1); /*-Q01*/ + } + else + { /*new remainder:*/ + R = R<<2)|((D>>(i+i))&3); + R = R+((Q<<2)|3); /*+Q11*/ + } + if (R>=0) Q = Q<<1)|1; /*new Q:*/ + else Q = Q<<1)|0; /*new Q:*/ + } + + /*remainder adjusting*/ + if (R<0) R = R+((Q<<1)|1); + *r = R; /*return remainder*/ + return(Q); /*return root*/ +} + +From wikipedia page: + +short isqrt(short num) { + short res = 0; + short bit = 1 << 14; // The second-to-top bit is set: 1 << 30 for 32 bits + + // "bit" starts at the highest power of four <= the argument. + while (bit > num) + bit >>= 2; + + while (bit != 0) { + if (num >= res + bit) { + num -= res + bit; + res = (res >> 1) + bit; + } + else + res >>= 1; + bit >>= 2; + } + return res; +} + """