Changeset 516e780 in mainline for uspace/lib/math/generic/trunc.c

Timestamp:

2018-08-31T11:55:41Z (7 years ago)

Author:

GitHub <noreply@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

fa86fff

Parents:

7f7d642

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2018-08-31 11:55:41)

git-committer:

GitHub <noreply@…> (2018-08-31 11:55:41)

Message:

Strip down libmath. (#45)

libmath is mostly unused (except for trunc(), sin() and cos()), and most functions in it are either very imprecise or downright broken. Additionally, it is implemented in manner that conflicts with C standard. Instead of trying to fix all the shortcomings while maintaining unused functionality, I'm opting to simply remove most of it and only keep the parts that are currently necessary.

Later readdition of the removed functions is possible, but there needs to be a reliable way to evaluate their quality first.

File:

• uspace/lib/math/generic/trunc.c (modified) (3 diffs)

uspace/lib/math/generic/trunc.c

@@ -34 +34 @@
  */
 
-#include <mathtypes.h>
-#include <trunc.h>
+#include <math.h>
+#include <float.h>
+#include <stdint.h>
 
 /** Truncate fractional part (round towards zero)
@@ -52 +53 @@
  *
  */
-float32_t float32_trunc(float32_t val)
+float truncf(float val)
 {
-        float32_u v;
-        int32_t exp;
+        const int exp_bias = FLT_MAX_EXP - 1;
+        const int mant_bits = FLT_MANT_DIG - 1;
+        const uint32_t mant_mask = (UINT32_C(1) << mant_bits) - 1;
 
-        v.val = val;
-        exp = v.data.parts.exp - FLOAT32_BIAS;
+        union {
+                float f;
+                uint32_t i;
+        } u = { .f = fabsf(val) };
 
-        if (exp < 0) {
-                /* -1 < val < 1 => result is +0 or -0 */
-                v.data.parts.exp = 0;
-                v.data.parts.fraction = 0;
-        } else if (exp >= FLOAT32_FRACTION_SIZE) {
-                if (exp == 1024) {
-                        /* val is +inf, -inf or NaN => trigger an exception */
-                        // FIXME TODO
-                }
+        int exp = (u.i >> mant_bits) - exp_bias;
 
-                /* All bits in val are relevant for the result */
-        } else {
-                /* Truncate irrelevant fraction bits */
-                v.data.parts.fraction &= ~(UINT32_C(0x007fffff) >> exp);
-        }
+        /* If value is less than one, return zero with appropriate sign. */
+        if (exp < 0)
+                return copysignf(0.0f, val);
 
-        return v.val;
+        if (exp >= mant_bits)
+                return val;
+
+        /* Truncate irrelevant fraction bits */
+        u.i &= ~(mant_mask >> exp);
+        return copysignf(u.f, val);
 }
 
@@ -94 +93 @@
  *
  */
-float64_t float64_trunc(float64_t val)
+double trunc(double val)
 {
-        float64_u v;
-        int32_t exp;
+        const int exp_bias = DBL_MAX_EXP - 1;
+        const int mant_bits = DBL_MANT_DIG - 1;
+        const uint64_t mant_mask = (UINT64_C(1) << mant_bits) - 1;
 
-        v.val = val;
-        exp = v.data.parts.exp - FLOAT64_BIAS;
+        union {
+                double f;
+                uint64_t i;
+        } u = { .f = fabs(val) };
 
-        if (exp < 0) {
-                /* -1 < val < 1 => result is +0 or -0 */
-                v.data.parts.exp = 0;
-                v.data.parts.fraction = 0;
-        } else if (exp >= FLOAT64_FRACTION_SIZE) {
-                if (exp == 1024) {
-                        /* val is +inf, -inf or NaN => trigger an exception */
-                        // FIXME TODO
-                }
+        int exp = ((int)(u.i >> mant_bits)) - exp_bias;
 
-                /* All bits in val are relevant for the result */
-        } else {
-                /* Truncate irrelevant fraction bits */
-                v.data.parts.fraction &= ~(UINT64_C(0x000fffffffffffff) >> exp);
-        }
+        /* If value is less than one, return zero with appropriate sign. */
+        if (exp < 0)
+                return copysign(0.0, val);
 
-        return v.val;
+        if (exp >= mant_bits)
+                return val;
+
+        /* Truncate irrelevant fraction bits */
+        u.i &= ~(mant_mask >> exp);
+        return copysign(u.f, val);
 }