patch-2.4.23 linux-2.4.23/arch/m68k/math-emu/fp_log.c
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- Lines: 123
- Date:
2003-11-28 10:26:19.000000000 -0800
- Orig file:
linux-2.4.22/arch/m68k/math-emu/fp_log.c
- Orig date:
1999-08-15 11:47:29.000000000 -0700
diff -urN linux-2.4.22/arch/m68k/math-emu/fp_log.c linux-2.4.23/arch/m68k/math-emu/fp_log.c
@@ -17,10 +17,22 @@
#include "fp_emu.h"
+static const struct fp_ext fp_one =
+{
+ 0, 0, 0x3fff, { 0 }
+};
+
+extern struct fp_ext *fp_fadd(struct fp_ext *dest, const struct fp_ext *src);
+extern struct fp_ext *fp_fdiv(struct fp_ext *dest, const struct fp_ext *src);
+extern struct fp_ext *fp_fmul(struct fp_ext *dest, const struct fp_ext *src);
+
struct fp_ext *
fp_fsqrt(struct fp_ext *dest, struct fp_ext *src)
{
- uprint("fsqrt\n");
+ struct fp_ext tmp, src2;
+ int i, exp;
+
+ dprint(PINSTR, "fsqrt\n");
fp_monadic_check(dest, src);
@@ -34,6 +46,56 @@
if (IS_INF(dest))
return dest;
+ /*
+ * sqrt(m) * 2^(p) , if e = 2*p
+ * sqrt(m*2^e) =
+ * sqrt(2*m) * 2^(p) , if e = 2*p + 1
+ *
+ * So we use the last bit of the exponent to decide wether to
+ * use the m or 2*m.
+ *
+ * Since only the fractional part of the mantissa is stored and
+ * the integer part is assumed to be one, we place a 1 or 2 into
+ * the fixed point representation.
+ */
+ exp = dest->exp;
+ dest->exp = 0x3FFF;
+ if (!(exp & 1)) /* lowest bit of exponent is set */
+ dest->exp++;
+ fp_copy_ext(&src2, dest);
+
+ /*
+ * The taylor row arround a for sqrt(x) is:
+ * sqrt(x) = sqrt(a) + 1/(2*sqrt(a))*(x-a) + R
+ * With a=1 this gives:
+ * sqrt(x) = 1 + 1/2*(x-1)
+ * = 1/2*(1+x)
+ */
+ fp_fadd(dest, &fp_one);
+ dest->exp--; /* * 1/2 */
+
+ /*
+ * We now apply the newton rule to the function
+ * f(x) := x^2 - r
+ * which has a null point on x = sqrt(r).
+ *
+ * It gives:
+ * x' := x - f(x)/f'(x)
+ * = x - (x^2 -r)/(2*x)
+ * = x - (x - r/x)/2
+ * = (2*x - x + r/x)/2
+ * = (x + r/x)/2
+ */
+ for (i = 0; i < 9; i++) {
+ fp_copy_ext(&tmp, &src2);
+
+ fp_fdiv(&tmp, dest);
+ fp_fadd(dest, &tmp);
+ dest->exp--;
+ }
+
+ dest->exp += (exp - 0x3FFF) / 2;
+
return dest;
}
@@ -123,20 +185,39 @@
struct fp_ext *
fp_fgetexp(struct fp_ext *dest, struct fp_ext *src)
{
- uprint("fgetexp\n");
+ dprint(PINSTR, "fgetexp\n");
fp_monadic_check(dest, src);
+ if (IS_INF(dest)) {
+ fp_set_nan(dest);
+ return dest;
+ }
+ if (IS_ZERO(dest))
+ return dest;
+
+ fp_conv_long2ext(dest, (int)dest->exp - 0x3FFF);
+
+ fp_normalize_ext(dest);
+
return dest;
}
struct fp_ext *
fp_fgetman(struct fp_ext *dest, struct fp_ext *src)
{
- uprint("fgetman\n");
+ dprint(PINSTR, "fgetman\n");
fp_monadic_check(dest, src);
+ if (IS_ZERO(dest))
+ return dest;
+
+ if (IS_INF(dest))
+ return dest;
+
+ dest->exp = 0x3FFF;
+
return dest;
}
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