SkFloat.cpp revision bf0001d0472d727266762c5967ec0d919a6df083 
1
2/*
3 * Copyright 2008 The Android Open Source Project
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10#include "SkFloat.h"
11#include "SkMathPriv.h"
12
13#define EXP_BIAS    (127+23)
14
15static int get_unsigned_exp(uint32_t packed)
16{
17    return (packed << 1 >> 24);
18}
19
20static unsigned get_unsigned_value(uint32_t packed)
21{
22    return (packed << 9 >> 9) | (1 << 23);
23}
24
25static int get_signed_value(int32_t packed)
26{
27    return SkApplySign(get_unsigned_value(packed), SkExtractSign(packed));
28}
29
30/////////////////////////////////////////////////////////////////////////
31
32int SkFloat::GetShift(int32_t packed, int shift)
33{
34    if (packed == 0)
35        return 0;
36
37    int exp = get_unsigned_exp(packed) - EXP_BIAS - shift;
38    int value = get_unsigned_value(packed);
39
40    if (exp >= 0)
41    {
42        if (exp > 8)    // overflow
43            value = SK_MaxS32;
44        else
45            value <<= exp;
46    }
47    else
48    {
49        exp = -exp;
50        if (exp > 23)   // underflow
51            value = 0;
52        else
53            value >>= exp;
54    }
55    return SkApplySign(value, SkExtractSign(packed));
56}
57
58/////////////////////////////////////////////////////////////////////////////////////
59
60int32_t SkFloat::SetShift(int value, int shift)
61{
62    if (value == 0)
63        return 0;
64
65    // record the sign and make value positive
66    int sign = SkExtractSign(value);
67    value = SkApplySign(value, sign);
68
69    if (value >> 24)    // value is too big (has more than 24 bits set)
70    {
71        int bias = 8 - SkCLZ(value);
72        SkASSERT(bias > 0 && bias < 8);
73        value >>= bias;
74        shift += bias;
75    }
76    else
77    {
78        int zeros = SkCLZ(value << 8);
79        SkASSERT(zeros >= 0 && zeros <= 23);
80        value <<= zeros;
81        shift -= zeros;
82    }
83    // now value is left-aligned to 24 bits
84    SkASSERT((value >> 23) == 1);
85
86    shift += EXP_BIAS;
87    if (shift < 0)  // underflow
88        return 0;
89    else
90    {
91        if (shift > 255)    // overflow
92        {
93            shift = 255;
94            value = 0x00FFFFFF;
95        }
96        int32_t packed = sign << 31;        // set the sign-bit
97        packed |= shift << 23;          // store the packed exponent
98        packed |= ((unsigned)(value << 9) >> 9);    // clear 24th bit of value (its implied)
99
100#ifdef SK_DEBUG
101        {
102            int n;
103
104            n = SkExtractSign(packed);
105            SkASSERT(n == sign);
106            n = get_unsigned_exp(packed);
107            SkASSERT(n == shift);
108            n = get_unsigned_value(packed);
109            SkASSERT(n == value);
110        }
111#endif
112        return packed;
113    }
114}
115
116int32_t SkFloat::Neg(int32_t packed)
117{
118    if (packed)
119        packed = packed ^ (1 << 31);
120    return packed;
121}
122
123int32_t SkFloat::Add(int32_t packed_a, int32_t packed_b)
124{
125    if (packed_a == 0)
126        return packed_b;
127    if (packed_b == 0)
128        return packed_a;
129
130    int exp_a = get_unsigned_exp(packed_a);
131    int exp_b = get_unsigned_exp(packed_b);
132    int exp_diff = exp_a - exp_b;
133
134    int shift_a = 0, shift_b = 0;
135    int exp;
136
137    if (exp_diff >= 0)
138    {
139        if (exp_diff > 24)  // B is too small to contribute
140            return packed_a;
141        shift_b = exp_diff;
142        exp = exp_a;
143    }
144    else
145    {
146        exp_diff = -exp_diff;
147        if (exp_diff > 24)  // A is too small to contribute
148            return packed_b;
149        shift_a = exp_diff;
150        exp = exp_b;
151    }
152
153    int value_a = get_signed_value(packed_a) >> shift_a;
154    int value_b = get_signed_value(packed_b) >> shift_b;
155
156    return SkFloat::SetShift(value_a + value_b, exp - EXP_BIAS);
157}
158
159static inline int32_t mul24(int32_t a, int32_t b) {
160    int64_t tmp = (sk_64_mul(a, b) + (1 << 23)) >> 24;
161    return sk_64_asS32(tmp);
162}
163
164int32_t SkFloat::Mul(int32_t packed_a, int32_t packed_b)
165{
166    if (packed_a == 0 || packed_b == 0)
167        return 0;
168
169    int exp_a = get_unsigned_exp(packed_a);
170    int exp_b = get_unsigned_exp(packed_b);
171
172    int value_a = get_signed_value(packed_a);
173    int value_b = get_signed_value(packed_b);
174
175    return SkFloat::SetShift(mul24(value_a, value_b), exp_a + exp_b - 2*EXP_BIAS + 24);
176}
177
178int32_t SkFloat::MulInt(int32_t packed, int n)
179{
180    return Mul(packed, SetShift(n, 0));
181}
182
183int32_t SkFloat::Div(int32_t packed_n, int32_t packed_d)
184{
185    SkASSERT(packed_d != 0);
186
187    if (packed_n == 0)
188        return 0;
189
190    int exp_n = get_unsigned_exp(packed_n);
191    int exp_d = get_unsigned_exp(packed_d);
192
193    int value_n = get_signed_value(packed_n);
194    int value_d = get_signed_value(packed_d);
195
196    return SkFloat::SetShift(SkDivBits(value_n, value_d, 24), exp_n - exp_d - 24);
197}
198
199int32_t SkFloat::DivInt(int32_t packed, int n)
200{
201    return Div(packed, SetShift(n, 0));
202}
203
204int32_t SkFloat::Invert(int32_t packed)
205{
206    return Div(packed, SetShift(1, 0));
207}
208
209int32_t SkFloat::Sqrt(int32_t packed)
210{
211    if (packed < 0)
212    {
213        SkDEBUGFAIL("can't sqrt a negative number");
214        return 0;
215    }
216
217    int exp = get_unsigned_exp(packed);
218    int value = get_unsigned_value(packed);
219
220    int nexp = exp - EXP_BIAS;
221    int root = SkSqrtBits(value << (nexp & 1), 26);
222    nexp >>= 1;
223    return SkFloat::SetShift(root, nexp - 11);
224}
225
226#if defined _WIN32 && _MSC_VER >= 1300  // disable warning : unreachable code
227#pragma warning ( push )
228#pragma warning ( disable : 4702 )
229#endif
230
231int32_t SkFloat::CubeRoot(int32_t packed)
232{
233    sk_throw();
234    return 0;
235}
236
237#if defined _WIN32 && _MSC_VER >= 1300
238#pragma warning ( pop )
239#endif
240
241static inline int32_t clear_high_bit(int32_t n)
242{
243    return ((uint32_t)(n << 1)) >> 1;
244}
245
246static inline int int_sign(int32_t a, int32_t b)
247{
248    return a > b ? 1 : (a < b ? -1 : 0);
249}
250
251int SkFloat::Cmp(int32_t packed_a, int32_t packed_b)
252{
253    packed_a = SkApplySign(clear_high_bit(packed_a), SkExtractSign(packed_a));
254    packed_b = SkApplySign(clear_high_bit(packed_b), SkExtractSign(packed_b));
255
256    return int_sign(packed_a, packed_b);
257}
258
259/////////////////////////////////////////////////////////////////////////////////////
260/////////////////////////////////////////////////////////////////////////////////////
261
262#ifdef SK_DEBUG
263
264#include "SkRandom.h"
265#include "SkFloatingPoint.h"
266
267void SkFloat::UnitTest()
268{
269#if 0 // def SK_SUPPORT_UNITTEST
270    SkFloat a, b, c, d;
271    int     n;
272
273    a.setZero();
274    n = a.getInt();
275    SkASSERT(n == 0);
276
277    b.setInt(5);
278    n = b.getInt();
279    SkASSERT(n == 5);
280
281    c.setInt(-3);
282    n = c.getInt();
283    SkASSERT(n == -3);
284
285    d.setAdd(c, b);
286    SkDebugf("SkFloat: %d + %d = %d\n", c.getInt(), b.getInt(), d.getInt());
287
288    SkRandom    rand;
289
290    int i;
291    for (i = 0; i < 1000; i++)
292    {
293        float fa, fb;
294        int aa = rand.nextS() >> 14;
295        int bb = rand.nextS() >> 14;
296        a.setInt(aa);
297        b.setInt(bb);
298        SkASSERT(a.getInt() == aa);
299        SkASSERT(b.getInt() == bb);
300
301        c.setAdd(a, b);
302        int cc = c.getInt();
303        SkASSERT(cc == aa + bb);
304
305        c.setSub(a, b);
306        cc = c.getInt();
307        SkASSERT(cc == aa - bb);
308
309        aa >>= 5;
310        bb >>= 5;
311        a.setInt(aa);
312        b.setInt(bb);
313        c.setMul(a, b);
314        cc = c.getInt();
315        SkASSERT(cc == aa * bb);
316        /////////////////////////////////////
317
318        aa = rand.nextS() >> 11;
319        a.setFixed(aa);
320        cc = a.getFixed();
321        SkASSERT(aa == cc);
322
323        bb = rand.nextS() >> 11;
324        b.setFixed(bb);
325        cc = b.getFixed();
326        SkASSERT(bb == cc);
327
328        cc = SkFixedMul(aa, bb);
329        c.setMul(a, b);
330        SkFixed dd = c.getFixed();
331        int diff = cc - dd;
332        SkASSERT(SkAbs32(diff) <= 1);
333
334        fa = (float)aa / 65536.0f;
335        fb = (float)bb / 65536.0f;
336        a.assertEquals(fa);
337        b.assertEquals(fb);
338        fa = a.getFloat();
339        fb = b.getFloat();
340
341        c.assertEquals(fa * fb, 1);
342
343        c.setDiv(a, b);
344        cc = SkFixedDiv(aa, bb);
345        dd = c.getFixed();
346        diff = cc - dd;
347        SkASSERT(SkAbs32(diff) <= 3);
348
349        c.assertEquals(fa / fb, 1);
350
351        SkASSERT((aa == bb) == (a == b));
352        SkASSERT((aa != bb) == (a != b));
353        SkASSERT((aa < bb) == (a < b));
354        SkASSERT((aa <= bb) == (a <= b));
355        SkASSERT((aa > bb) == (a > b));
356        SkASSERT((aa >= bb) == (a >= b));
357
358        if (aa < 0)
359        {
360            aa = -aa;
361            fa = -fa;
362        }
363        a.setFixed(aa);
364        c.setSqrt(a);
365        cc = SkFixedSqrt(aa);
366        dd = c.getFixed();
367        SkASSERT(dd == cc);
368
369        c.assertEquals(sk_float_sqrt(fa), 2);
370
371        // cuberoot
372#if 0
373        a.setInt(1);
374        a.cubeRoot();
375        a.assertEquals(1.0f, 0);
376        a.setInt(8);
377        a.cubeRoot();
378        a.assertEquals(2.0f, 0);
379        a.setInt(27);
380        a.cubeRoot();
381        a.assertEquals(3.0f, 0);
382#endif
383    }
384#endif
385}
386
387#endif
388