diff options
Diffstat (limited to 'drivers/gpu/drm/radeon/r600_blit_kms.c')
| -rw-r--r-- | drivers/gpu/drm/radeon/r600_blit_kms.c | 35 |
1 files changed, 25 insertions, 10 deletions
diff --git a/drivers/gpu/drm/radeon/r600_blit_kms.c b/drivers/gpu/drm/radeon/r600_blit_kms.c index d996f438113..accc032c103 100644 --- a/drivers/gpu/drm/radeon/r600_blit_kms.c +++ b/drivers/gpu/drm/radeon/r600_blit_kms.c @@ -468,27 +468,42 @@ set_default_state(struct radeon_device *rdev) radeon_ring_write(ring, sq_stack_resource_mgmt_2); } +#define I2F_MAX_BITS 15 +#define I2F_MAX_INPUT ((1 << I2F_MAX_BITS) - 1) +#define I2F_SHIFT (24 - I2F_MAX_BITS) + +/* + * Converts unsigned integer into 32-bit IEEE floating point representation. + * Conversion is not universal and only works for the range from 0 + * to 2^I2F_MAX_BITS-1. Currently we only use it with inputs between + * 0 and 16384 (inclusive), so I2F_MAX_BITS=15 is enough. If necessary, + * I2F_MAX_BITS can be increased, but that will add to the loop iterations + * and slow us down. Conversion is done by shifting the input and counting + * down until the first 1 reaches bit position 23. The resulting counter + * and the shifted input are, respectively, the exponent and the fraction. + * The sign is always zero. + */ static uint32_t i2f(uint32_t input) { u32 result, i, exponent, fraction; - if ((input & 0x3fff) == 0) - result = 0; /* 0 is a special case */ + WARN_ON_ONCE(input > I2F_MAX_INPUT); + + if ((input & I2F_MAX_INPUT) == 0) + result = 0; 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++) { + exponent = 126 + I2F_MAX_BITS; + fraction = (input & I2F_MAX_INPUT) << I2F_SHIFT; + + for (i = 0; i < I2F_MAX_BITS; i++) { if (fraction & 0x800000) break; else { - fraction = fraction << 1; /* keep - shifting left until top bit = 1 */ + fraction = fraction << 1; exponent = exponent - 1; } } - result = exponent << 23 | (fraction & 0x7fffff); /* mask - off top bit; assumed 1 */ + result = exponent << 23 | (fraction & 0x7fffff); } return result; } |