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author | Steven Fuerst <svfuerst@gmail.com> | 2012-08-15 15:07:15 -0700 |
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committer | Alex Deucher <alexander.deucher@amd.com> | 2012-09-20 13:10:34 -0400 |
commit | 747f49ba67b8895a5831ab539de551b916f3738c (patch) | |
tree | b1b1561ae97f9f7fdab8ae44e019bd5dca0e62e4 /drivers/gpu/drm/radeon/r600_blit.c | |
parent | 7ff64fcaa7b7ba62d12758e49643f31dd9e90ece (diff) | |
download | op-kernel-dev-747f49ba67b8895a5831ab539de551b916f3738c.zip op-kernel-dev-747f49ba67b8895a5831ab539de551b916f3738c.tar.gz |
Replace int2float() with an optimized version.
We use __fls() to find the most significant bit. Using that, the
loop can be avoided. A second trick is to use the behaviour of the
rotate instructions to expand the range of the unsigned int to float
conversion to the full 32 bits in a branchless way.
The routine is now exact up to 2^24. Above that, we truncate which
is equivalent to rounding towards zero.
Signed-off-by: Steven Fuerst <svfuerst@gmail.com>
Diffstat (limited to 'drivers/gpu/drm/radeon/r600_blit.c')
-rw-r--r-- | drivers/gpu/drm/radeon/r600_blit.c | 51 |
1 files changed, 28 insertions, 23 deletions
diff --git a/drivers/gpu/drm/radeon/r600_blit.c b/drivers/gpu/drm/radeon/r600_blit.c index ee1b815..7d8ac42 100644 --- a/drivers/gpu/drm/radeon/r600_blit.c +++ b/drivers/gpu/drm/radeon/r600_blit.c @@ -489,31 +489,36 @@ set_default_state(drm_radeon_private_t *dev_priv) ADVANCE_RING(); } -uint32_t int2float(uint32_t input) +/* 23 bits of float fractional data */ +#define I2F_FRAC_BITS 23 +#define I2F_MASK ((1 << I2F_FRAC_BITS) - 1) + +/* + * Converts unsigned integer into 32-bit IEEE floating point representation. + * Will be exact from 0 to 2^24. Above that, we round towards zero + * as the fractional bits will not fit in a float. (It would be better to + * round towards even as the fpu does, but that is slower.) + */ +uint32_t int2float(uint32_t x) { - u32 result, i, exponent, fraction; - - if ((input & 0x3fff) == 0) - result = 0; /* 0 is a special case */ - else { - exponent = 140; /* exponent biased by 127; */ - fraction = (input & 0x3fff) << 10; /* cheat and only - handle numbers below 2^^15 */ - for (i = 0; i < 14; i++) { - if (fraction & 0x800000) - break; - else { - fraction = fraction << 1; /* keep - shifting left until top bit = 1 */ - exponent = exponent - 1; - } - } - result = exponent << 23 | (fraction & 0x7fffff); /* mask - off top bit; assumed 1 */ - } - return result; -} + uint32_t msb, exponent, fraction; + + /* Zero is special */ + if (!x) return 0; + + /* Get location of the most significant bit */ + msb = __fls(x); + /* + * Use a rotate instead of a shift because that works both leftwards + * and rightwards due to the mod(32) behaviour. This means we don't + * need to check to see if we are above 2^24 or not. + */ + fraction = ror32(x, (msb - I2F_FRAC_BITS) & 0x1f) & I2F_MASK; + exponent = (127 + msb) << I2F_FRAC_BITS; + + return fraction + exponent; +} static int r600_nomm_get_vb(struct drm_device *dev) { |