sp_sub.c 3.9 KB

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  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /* IEEE754 floating point arithmetic
  3. * single precision
  4. */
  5. /*
  6. * MIPS floating point support
  7. * Copyright (C) 1994-2000 Algorithmics Ltd.
  8. */
  9. #include "ieee754sp.h"
  10. union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y)
  11. {
  12. int s;
  13. COMPXSP;
  14. COMPYSP;
  15. EXPLODEXSP;
  16. EXPLODEYSP;
  17. ieee754_clearcx();
  18. FLUSHXSP;
  19. FLUSHYSP;
  20. switch (CLPAIR(xc, yc)) {
  21. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
  22. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
  23. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
  24. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
  25. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
  26. return ieee754sp_nanxcpt(y);
  27. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
  28. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
  29. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
  30. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
  31. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
  32. case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
  33. return ieee754sp_nanxcpt(x);
  34. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
  35. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
  36. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
  37. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
  38. return y;
  39. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
  40. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
  41. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
  42. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
  43. case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
  44. return x;
  45. /*
  46. * Infinity handling
  47. */
  48. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
  49. if (xs != ys)
  50. return x;
  51. ieee754_setcx(IEEE754_INVALID_OPERATION);
  52. return ieee754sp_indef();
  53. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
  54. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
  55. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
  56. return ieee754sp_inf(ys ^ 1);
  57. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
  58. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
  59. case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
  60. return x;
  61. /*
  62. * Zero handling
  63. */
  64. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
  65. if (xs != ys)
  66. return x;
  67. else
  68. return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
  69. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
  70. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
  71. return x;
  72. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
  73. case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
  74. /* quick fix up */
  75. SPSIGN(y) ^= 1;
  76. return y;
  77. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
  78. SPDNORMX;
  79. fallthrough;
  80. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
  81. SPDNORMY;
  82. break;
  83. case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
  84. SPDNORMX;
  85. break;
  86. case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
  87. break;
  88. }
  89. /* flip sign of y and handle as add */
  90. ys ^= 1;
  91. assert(xm & SP_HIDDEN_BIT);
  92. assert(ym & SP_HIDDEN_BIT);
  93. /* provide guard,round and stick bit space */
  94. xm <<= 3;
  95. ym <<= 3;
  96. if (xe > ye) {
  97. /*
  98. * have to shift y fraction right to align
  99. */
  100. s = xe - ye;
  101. ym = XSPSRS(ym, s);
  102. ye += s;
  103. } else if (ye > xe) {
  104. /*
  105. * have to shift x fraction right to align
  106. */
  107. s = ye - xe;
  108. xm = XSPSRS(xm, s);
  109. xe += s;
  110. }
  111. assert(xe == ye);
  112. assert(xe <= SP_EMAX);
  113. if (xs == ys) {
  114. /* generate 28 bit result of adding two 27 bit numbers
  115. */
  116. xm = xm + ym;
  117. if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */
  118. SPXSRSX1(); /* shift preserving sticky */
  119. }
  120. } else {
  121. if (xm >= ym) {
  122. xm = xm - ym;
  123. } else {
  124. xm = ym - xm;
  125. xs = ys;
  126. }
  127. if (xm == 0) {
  128. if (ieee754_csr.rm == FPU_CSR_RD)
  129. return ieee754sp_zero(1); /* round negative inf. => sign = -1 */
  130. else
  131. return ieee754sp_zero(0); /* other round modes => sign = 1 */
  132. }
  133. /* normalize to rounding precision
  134. */
  135. while ((xm >> (SP_FBITS + 3)) == 0) {
  136. xm <<= 1;
  137. xe--;
  138. }
  139. }
  140. return ieee754sp_format(xs, xe, xm);
  141. }