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Gets rid of a "safe" signed overflow in silk_DIV32_varQ()

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This commit is contained in:
Jean-Marc Valin 2011-10-11 16:47:00 -04:00
parent 3737862620
commit 4541bbcc22
2 changed files with 6 additions and 1 deletions
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3
silk/Inlines.h
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@ -117,7 +117,8 @@ static inline opus_int32 silk_DIV32_varQ( /* O returns a good approximatio
result = silk_SMULWB(a32_nrm, b32_inv); /* Q: 29 + a_headrm - b_headrm */
/* Compute residual by subtracting product of denominator and first approximation */
a32_nrm -= silk_LSHIFT( silk_SMMUL(b32_nrm, result), 3 ); /* Q: a_headrm */
/* It's OK to overflow because the final value of a32_nrm should always be small */
a32_nrm = silk_SUB32_ovflw(a32_nrm, silk_LSHIFT_ovflw( silk_SMMUL(b32_nrm, result), 3 )); /* Q: a_headrm */
/* Refinement */
result = silk_SMLAWB(result, a32_nrm, b32_inv); /* Q: 29 + a_headrm - b_headrm */

4
silk/SigProc_FIX.h
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@ -417,6 +417,9 @@ static inline opus_int32 silk_ROR32( opus_int32 a32, opus_int rot )
/* Adds two signed 32-bit values in a way that can overflow, while not relying on undefined behaviour
(just standard two's complement implementation-specific behaviour) */
#define silk_ADD32_ovflw(a, b) ((opus_int32)((opus_uint32)(a) + (opus_uint32)(b)))
/* Subtractss two signed 32-bit values in a way that can overflow, while not relying on undefined behaviour
(just standard two's complement implementation-specific behaviour) */
#define silk_SUB32_ovflw(a, b) ((opus_int32)((opus_uint32)(a) - (opus_uint32)(b)))
/* Multiply-accumulate macros that allow overflow in the addition (ie, no asserts in debug mode)*/
#define silk_MLA_ovflw(a32, b32, c32) silk_ADD32_ovflw((a32), (opus_uint32)(b32) * (opus_uint32)(c32))
@ -484,6 +487,7 @@ static inline opus_int32 silk_ROR32( opus_int32 a32, opus_int rot )
#define silk_LSHIFT_SAT32(a, shift) (silk_LSHIFT32( silk_LIMIT( (a), silk_RSHIFT32( silk_int32_MIN, (shift) ), \
silk_RSHIFT32( silk_int32_MAX, (shift) ) ), (shift) ))
#define silk_LSHIFT_ovflw(a, shift) ((opus_int32)((opus_uint32)(a)<<(shift))) /* shift >= 0, allowed to overflow */
#define silk_LSHIFT_uint(a, shift) ((a)<<(shift)) /* shift >= 0 */
#define silk_RSHIFT_uint(a, shift) ((a)>>(shift)) /* shift >= 0 */