[avr-libc-dev] [RFC] [bug #9348] asin (acos) & atan problem (64K boundary)

[Theodore A. Roth]

Hi,

I just did a cursory look at this bug to see if there was a simple fix.

It seems to me that moving the tables into a .c file would allow us to
have gcc force the table in the lower 64K. For example, the table_asin
defined as such in asin.S:

 table_asin: DCB 7
        DCB 0x75, 0xA5, 0x7A, 0x2C  ; P7
        DCB 0x77, 0x5A, 0x90, 0xC5  ; P6
        DCB 0x79, 0x8B, 0xFC, 0x66  ; P5
        DCB 0x79, 0x7D, 0x10, 0xF8  ; P4
        DCB 0x7A, 0xCD, 0x83, 0x92  ; P3
        DCB 0x7B, 0x36, 0x3A, 0x9E  ; P2
        DCB 0x7C, 0xDB, 0xBF, 0xCA  ; P1
        DCB 0x7F, 0x49, 0x0F, 0xDA  ; P0
        DCB 0x00                    ; 0.0

would be moved to table_asin.c like this

  #include <avr/pgmspace.h>
  #include <avr/stdint.h>

  uint8_t table_asin [] PROGMEM = {
      7,
      0x75, 0xA5, 0x7A, 0x2C,  /* P7 */
      0x77, 0x5A, 0x90, 0xC5,  /* P6 */
      0x79, 0x8B, 0xFC, 0x66,  /* P5 */
      0x79, 0x7D, 0x10, 0xF8,  /* P4 */
      0x7A, 0xCD, 0x83, 0x92,  /* P3 */
      0x7B, 0x36, 0x3A, 0x9E,  /* P2 */
      0x7C, 0xDB, 0xBF, 0xCA,  /* P1 */
      0x7F, 0x49, 0x0F, 0xDA,  /* P0 */
      0x00                     /* 0.0 */
  };

Then asin.S would need to have this added:

  extern table_asin

Does anyone see any flaws in this solution? I haven't had a chance to
do an experimental implementation yet.

Grepping through the avr-libc tree shows the problem to be more
expansive. I think all of these files will potentially have the problem:

  libm/fplib/atan.S
  libm/fplib/exp.S
  libm/fplib/fp_cosinus.S
  libm/fplib/strtod.S
  libm/fplib/log.S
  libm/fplib/tan.S
  libm/fplib/asin.S

Comments? Suggestions? Improvements?

---
Ted Roth
PGP Key ID: 0x18F846E9
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