target/m68k: implement flog2
Using a local m68k floatx80_log2()
[copied from previous:
Written by Andreas Grabher for Previous, NeXT Computer Emulator.]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180305203910.10391-6-laurent@vivier.eu>
diff --git a/target/m68k/softfloat.c b/target/m68k/softfloat.c
index 22fd7f6..9fa6d6f 100644
--- a/target/m68k/softfloat.c
+++ b/target/m68k/softfloat.c
@@ -715,3 +715,70 @@
return a;
}
+
+/*----------------------------------------------------------------------------
+ | Log base 2
+ *----------------------------------------------------------------------------*/
+
+floatx80 floatx80_log2(floatx80 a, float_status *status)
+{
+ flag aSign;
+ int32_t aExp;
+ uint64_t aSig;
+
+ int8_t user_rnd_mode, user_rnd_prec;
+
+ floatx80 fp0, fp1;
+
+ aSig = extractFloatx80Frac(a);
+ aExp = extractFloatx80Exp(a);
+ aSign = extractFloatx80Sign(a);
+
+ if (aExp == 0x7FFF) {
+ if ((uint64_t) (aSig << 1)) {
+ propagateFloatx80NaNOneArg(a, status);
+ }
+ if (aSign == 0) {
+ return packFloatx80(0, floatx80_infinity.high,
+ floatx80_infinity.low);
+ }
+ }
+
+ if (aExp == 0) {
+ if (aSig == 0) {
+ float_raise(float_flag_divbyzero, status);
+ return packFloatx80(1, floatx80_infinity.high,
+ floatx80_infinity.low);
+ }
+ normalizeFloatx80Subnormal(aSig, &aExp, &aSig);
+ }
+
+ if (aSign) {
+ float_raise(float_flag_invalid, status);
+ return floatx80_default_nan(status);
+ }
+
+ user_rnd_mode = status->float_rounding_mode;
+ user_rnd_prec = status->floatx80_rounding_precision;
+ status->float_rounding_mode = float_round_nearest_even;
+ status->floatx80_rounding_precision = 80;
+
+ if (aSig == one_sig) { /* X is 2^k */
+ status->float_rounding_mode = user_rnd_mode;
+ status->floatx80_rounding_precision = user_rnd_prec;
+
+ a = int32_to_floatx80(aExp - 0x3FFF, status);
+ } else {
+ fp0 = floatx80_logn(a, status);
+ fp1 = packFloatx80(0, 0x3FFF, LIT64(0xB8AA3B295C17F0BC)); /* INV_L2 */
+
+ status->float_rounding_mode = user_rnd_mode;
+ status->floatx80_rounding_precision = user_rnd_prec;
+
+ a = floatx80_mul(fp0, fp1, status); /* LOGN(X)*INV_L2 */
+ }
+
+ float_raise(float_flag_inexact, status);
+
+ return a;
+}
