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avcodec/fate-idct8x8: Defined behavior: eliminate negative left-shifts.

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The original code left-shifts negative values, which is undefined
in the C99 specification (the one used during normal FFmpeg compilation).
This change multiplies by (1 << shift), which is functionally equivalent,
but has defined behavior.
With this change, fate-idct8x8 compiled with --fsanitize=undefined works.

Bug-Id: 686

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

The assembly generated by gcc is unchanged by this commit
pull/68/head^2
Katerina Barone-Adesi 11 years ago committed by Michael Niedermayer
parent 7d25af1547
commit e50ae60d46
3 changed files with 25 additions and 25 deletions
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  1. 4
      libavcodec/jfdctint_template.c
  2. 36
      libavcodec/jrevdct.c
  3. 10
      libavcodec/simple_idct_template.c

4
libavcodec/jfdctint_template.c
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@ -216,8 +216,8 @@ static av_always_inline void FUNC(row_fdct)(int16_t *data)
tmp11 = tmp1 + tmp2;
tmp12 = tmp1 - tmp2;
dataptr[0] = (int16_t) ((tmp10 + tmp11) << PASS1_BITS);
dataptr[4] = (int16_t) ((tmp10 - tmp11) << PASS1_BITS);
dataptr[0] = (int16_t) ((tmp10 + tmp11) * (1 << PASS1_BITS));
dataptr[4] = (int16_t) ((tmp10 - tmp11) * (1 << PASS1_BITS));
z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
dataptr[2] = (int16_t) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),

36
libavcodec/jrevdct.c
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@ -249,8 +249,8 @@ void ff_j_rev_dct(DCTBLOCK data)
/* AC terms all zero */
if (d0) {
/* Compute a 32 bit value to assign. */
int16_t dcval = (int16_t) (d0 << PASS1_BITS);
register int v = (dcval & 0xffff) | ((dcval << 16) & 0xffff0000);
int16_t dcval = (int16_t) (d0 * (1 << PASS1_BITS));
register int v = (dcval & 0xffff) | ((dcval * (1 << 16)) & 0xffff0000);
idataptr[0] = v;
idataptr[1] = v;
@ -272,8 +272,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -284,8 +284,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = MULTIPLY(-d6, FIX_1_306562965);
tmp3 = MULTIPLY(d6, FIX_0_541196100);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -298,8 +298,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = MULTIPLY(d2, FIX_0_541196100);
tmp3 = MULTIPLY(d2, FIX_1_306562965);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -307,8 +307,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp12 = tmp1 - tmp2;
} else {
/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
tmp10 = tmp13 = (d0 + d4) * CONST_SCALE;
tmp11 = tmp12 = (d0 - d4) * CONST_SCALE;
}
}
@ -618,8 +618,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -630,8 +630,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = MULTIPLY(-d6, FIX_1_306562965);
tmp3 = MULTIPLY(d6, FIX_0_541196100);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -644,8 +644,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp2 = MULTIPLY(d2, FIX_0_541196100);
tmp3 = MULTIPLY(d2, FIX_1_306562965);
tmp0 = (d0 + d4) << CONST_BITS;
tmp1 = (d0 - d4) << CONST_BITS;
tmp0 = (d0 + d4) * CONST_SCALE;
tmp1 = (d0 - d4) * CONST_SCALE;
tmp10 = tmp0 + tmp3;
tmp13 = tmp0 - tmp3;
@ -653,8 +653,8 @@ void ff_j_rev_dct(DCTBLOCK data)
tmp12 = tmp1 - tmp2;
} else {
/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
tmp10 = tmp13 = (d0 + d4) * CONST_SCALE;
tmp11 = tmp12 = (d0 - d4) * CONST_SCALE;
}
}

10
libavcodec/simple_idct_template.c
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@ -110,12 +110,12 @@ static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
if (((((uint64_t *)row)[0] & ~ROW0_MASK) | ((uint64_t *)row)[1]) == 0) {
uint64_t temp;
if (DC_SHIFT - extra_shift >= 0) {
temp = (row[0] << (DC_SHIFT - extra_shift)) & 0xffff;
temp = (row[0] * (1 << (DC_SHIFT - extra_shift))) & 0xffff;
} else {
temp = ((row[0] + (1<<(extra_shift - DC_SHIFT-1))) >> (extra_shift - DC_SHIFT)) & 0xffff;
}
temp += temp << 16;
temp += temp << 32;
temp += temp * (1 << 16);
temp += temp * ((uint64_t) 1 << 32);
((uint64_t *)row)[0] = temp;
((uint64_t *)row)[1] = temp;
return;
@ -127,11 +127,11 @@ static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
row[1])) {
uint32_t temp;
if (DC_SHIFT - extra_shift >= 0) {
temp = (row[0] << (DC_SHIFT - extra_shift)) & 0xffff;
temp = (row[0] * (1 << (DC_SHIFT - extra_shift))) & 0xffff;
} else {
temp = ((row[0] + (1<<(extra_shift - DC_SHIFT-1))) >> (extra_shift - DC_SHIFT)) & 0xffff;
}
temp += temp << 16;
temp += temp * (1 << 16);
((uint32_t*)row)[0]=((uint32_t*)row)[1] =
((uint32_t*)row)[2]=((uint32_t*)row)[3] = temp;
return;

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